ENGINEERING 'LIBRARY 


Practical  Marine  Engineering 


FOR 


MARINE  ENGINEERS    AND  STUDENTS 


WITH 


Aids  for  Applicants  for  Marine    Engineers'  Licenses 


By  WILLIAM  F.  DURAND 

PROFESSOR  OF  MARINE  ENGINEERING,  CORNELL  UNIVERSITY. 


New  York 

Marine  Engineering,  Inc. 

309  Broadway 

1901 


o 


ENGINEERING 

Copyright,  1901 
By  MARINE  ENGINEERING,  Inc. 


Preface. 

A  I  \HE  purpose  of  the  author  in  the  preparation  of  this  work 
has  been  to  provide  help  for  the  operative  or  practical 
marine  engineer,  either  for  the  man  who  has  already  en- 
tered the  profession,  but  who  may  wish  to  perfect  himself  more 
fully  in  many  branches  of  the  subject,  or  for  the  applicant  for  the 
lowest  round  of  the  ladder,  or  for  the  young  man  whose  atten- 
tion is  first  turning  to  this  field,  and  who  may  wish  some  simple 
and  fairly  complete  presentation  of  the  subject  from  the  prac- 
tical standpoint. 

The  treatment  of  the  subject  throughout  has  thus  been  with 
a  view  to  simplicity,  but  without  undue  sacrifice  of  generality  or 
exactness  of  statement.  It  has  been  the  desire  of  the  author  to 
bring  the  subject,  so  far  as  treated  in  the  present  work,  within 
the  grasp  of  those  who  have  not  had  the  advantages  of  higher 
mathematical  and  engineering  education,  but  who  may  wish, 
nevertheless,  to  fit  themselves  for  positions  of  honor  and  respon- 
sibility in  the  field  of  operative  marine  engineering. 

With  this  end  in  view  only  such  parts  of  the  general  field  of 
engineering  have  been  included  as  are  of  special  interest  to 
the  practical  marine  engineer.  On  these  topics,  however,  the 
attempt  has  been  made  to  give  the  largest  amount  of  useful  in- 
formation in  the  simplest  and  most  compact  form.  In  the  ma- 
rine field  itself  likewise,  selection  has  been  necessary,  and 
many  interesting  parts  of  the  subject  have  been  omitted  or 
briefly  referred  to  in  order  to  give  more  room  for  the  practical 
side  of  the  subject.  Thus  the  book  does  not  treat  of  the  de- 
signing of  marine  machinery  except  in  an  incidental  way.  For 
the  operative  engineer  the  topics  of  greater  importance  are  con- 
struction, operation,  management  and  care.  The  simpler  parts 
of  the  subject  of  design  are,  however,  represented  by  the  U.  S. 

Hi. 

836454 


PREFACE. 

rules  regarding  the  design  and  construction  of  marine  boilers, 
and  by  many  hints  regarding  proportions  and  relations  scat- 
tered throughout  the  work. 

In  the  chapters  dealing  descriptively  with  engines,  .boilers 
and  auxiliaries,  it  has  been  impossible  of  course,  to  describe  ex- 
haustively every  form  of  design  or  appliance  to  be  met  with 
in  marine  practice.  The  purpose  has  been  rather  to  describe 
typical  or  standard  forms,  and  to  give  the  general  conditions 
which  the  various  parts  must  fulfil.  The  illustrations  have  been 
specially  chosen  with  a  view  to  supplement  the  text  in  these 
various  particulars,  and  it  is  hoped  that  they  will  form  not  the 
least  instructive  and  acceptable  feature  of  the  work. 

The  subject  of  operation,  management  and  repair  has  been 
given  special  attention,  and  it  is  hoped  that  this  part  of  the  work 
will  be  of  value,  especially  to  the  young  engineer  lacking  in 
practical  experience. 

In  Chapter  VIII  is  gathered  a  collection  of  miscellaneous 
problems  and  discussions,  many  of  which,  it  is  hoped,  will  be  of 
value  to  the  professional  engineer  in  connection  with  the  vari- 
ous questions  likely  to  arise  in  his  experience.  The  chapters 
on  valve  gears  and  on  indicator  cards  while  necessarily  brief  are 
intended  to  present  the  fundamental  features  of  the  subject  in 
such  manner  as  to  aid  the  novice  and  instruct  and  stimulate 
the  professional  engineer  to  a  better  understanding  of  these  im- 
portant branches  of  the  subject.  The  chapter  on  propulsion 
and  powering  is  necessarily  brief,  but  the  fundamental  principles 
are  given,  with  a  few  simple  rules  and  the  discussion  of  most  of 
the  problems  commonly  arising  in  practical  engineering  work. 

The  chapters  on  refrigeration  and  on  electricity  on  shipboard 
are  added  in  order  to  give  the  marine  engineer  some  notion  of 
the  fundamental  principles  controlling  the  operation  of  refrig- 
erating and  electric  machinery,  these  two  important  auxiliaries 
of  modern  marine  engineering  practice.  They  are  of  necessity 
quite  incomplete,  especially  Chapter  XII,  but  it  is  hoped  that 
nevertheless  they  may  be  of  aid  to  the  marine  engineer  in  un- 
derstanding the  mode  of  operation  of  such  machinery,  and  in 
giving  to  it  the  proper  care. 

In  Part  II  is  given  an  elementary  discussion  of  computa- 
tions for  engineers,  or  rather  of  the  mathematics  upon  \vhich 
such  computations  depend.  A  general  knowledge  of  the  sub- 
ject is  pre-supposed,  but  the  more  essential  features  of  the  ele- 

iv 


PREFACE. 

mentary  mathematics  usually  required  are  given  and  illustrated 
with  many  problems.  It  is  hoped  that  this  feature  of  the  work 
may  be  of  aid  to  those  who  wish  to  drill  themselves  in  such  com- 
putations as  the  marine  engineer  is  commonly  called  upon  to 
make. 

Attention  may  also  be  called  to  the  appendix  containing  a  list 
of  questions,  each  with  page  reference  to  the  part  of  the  book 
where  the  answer  may  be  found.  The  answer,  of  course,  will 
not  usually  be  found  in  the  direct  form  suggested  by  the  ques- 
tion, but  a  discussion  of  the  subject  will  be  found  giving  the  in- 
formation needed  for  the  answer,  which  may  be  put  into  form 
by  the  reader  for  himself.  It  is  believed  that  such  an  exercise 
will  be  of  far  greater  value  than  the  perusal  of  a  series  of  ques- 
tions and  answers  in  the  usual  catechism  form. 

Throughout  the  work  numerous  problems  have  been  scat- 
tered, accompanied  usually  by  illustrative  examples,  showing 
the  method  of  working.  Numerous  cross  references  have  also 
been  given,  to  aid  in  the  more  complete  explanation  of  any 
given  topic,  and  in  finding  these  use  should  be  made  of  the  table 
of  contents,  giving  the  page  location  of  each  section  and  bracket 
subdivision. 

A  collection  of  miscellaneous  problems  is  also  added  at  the 
end  of  the  book,  as  well  as  a  set  of  steam  tables  for  use  in  the  so- 
lution of  the  various  problems  requiring  a  knowledge  of  its  vari- 
ous mechanical  and  physical  properties. 


CONTENTS. 


Contents 


CHAPTER  I. 


Principal  Materials  of  Engineering  Construction. 

5ECTION.  PAGE. 

1.  Aluminum    I 

2.  Antimony    I 

3.  Bismuth    2 

4.  Copper    2 

5.  Iron   and   Steel 3 

i  ]     Cast  Iron   4 

2]     Malleable  Iron   9 

3  Wrought    Iron    10 

4  Blisters  and  Laminations   u 

5  Steel   12 

6.  Lead 23 

7.  Tin    24 

8.  Zinc     24 

9.  Alloys  24 

10.  The  Testing  of  Metals   ' 26 

i  ]     Different  Kinds  of  Tests   26 

2]     Explanation  of  Terms  Used   26 

3]     Test  Pieces  for  Iron    28 

4      Test  Pieces  for  Steel  and  Other  Materials   28 

5]     Bending,  Quenching  and  Hammer  Tests  29 

CHAPTER  II. 

Fuels. 

11.  Coa! 3i 

i]     Composition  and  General  Properties   31 

2]     Combustion    •  32 

3]     Impurities  in  Coal.    Clinker  Formation 35 

4]     Weathering  of  Coal 36 

5]     Spontaneous  Combustion 37 

6]     Corrosion    4° 

7!     Transportation  and  Stowage \  •  40 

8]     General   Comparison   Between   Bituminous  and  Anthracite 

Coal    4i 

12.  Briquettes  and  Artificial   Fuel    41 

13.  Liquid  Fuel   42 

i  ]     Composition 42 

2]     Combustion    43 

"3!     Danger  of  Explosion  : 44 

4]     Evaporative  Power 44 

"5l     Stowage  and  Handling   45 

6]     Use  of  Oil  and  Coal  Combined   46 

7]     Cost  46 

vii. 


CONTENTS. 


CHAPTER  III. 


Boilers. 

ON.  PAGE. 

14.  Types  of  Boilers   47 

i  ]     The  Scotch  Boiler 50 

2]     Direct  Tubular  Boiler,  Gunboat  Type  50 

Direct  Tubular  Boiler,  Locomotive  Type 51 

The  Flue  and  Return  Tubular  or  Leg  Boiler 51 

5J     The  Flue  Boiler  52 

:6n     Water-Tube  Boilers   53 

7]     Relative  Advantages  of  Different  Types  of  Boilers 56 

15.  Riveted  Joints    67 

16.  Materials  and  Construction  86 

i  ]     Materials  86 

2]     Joints   86 

3]     Construction  of  Fire-Tube  Boilers 87 

4]     Construction  of  Water-Tube  Boilers  . 108 

5]     Common  Sizes  and  Dimensions  of  Scotch  Boilers 112 

'6]     Common  Proportions  for  Scotch  Boilers  112 

7]     Weights  of  Boilers   112 

8      Western  River  Boat  or  Flue  Boilers 113 

17.  Boiler  Mountings  and  Fire  Room  Fittings 115 

i]     Safety  Valves IIS 

2]     Muffler  118 

3]     Stop  Valve   n8 

4]     Dry-Pipe,  or  Internal  Steam  Pipe 120 

'5       Feed  Check  Valve  and  Internal  Feed  Pipe   121 

Surface  and   Bottom  Blows    122 

7      Steam  Gauges  124 

Water   Gauge   and    Cocks    125 

[9]     Hydrokineter 127 

[10]     Hydrometer   127 

[III      Boiler   Saddles    128 

[12       Boiler  Lagging 129 

18.  Draft 129 

19.  Boiler  Design  in  Accordance  with  the  Rules  of  the  U.  S.  Board 

of  Supervising  Inspectors  of  Steam  Vessels ,  138 

CHAPTER  IV. 

Marine  Engines. 

20.  Types  of  Engines  and  Arrangement  of  Parts 154 

21.  Description  of  Principal  Parts  of  a  Marine  Engine 165 

[i]     Cylinders  165 

"2]     Columns    168 

31     Bed-Plates    172 

'4!     Engine  Seating  174 

5]     Pistons  175 

6]     Piston-Rods  179 

7]     Crossheads    180 

8]     Connecting-Rods   184 

9]     Crank  Shafts   185 

[10]     Line  Thrust  and  Propeller  Shafts    188 

[nl     Bearings    190 

22.  Western   River   Practice 199 

23.  The    Steam    Turbine    207 

24.  Engine   Fittings    209 

f  i  ]     Throttle  Valve    209 

\2\     Main  Stop  Valve 212 

[3]     Cylinder  Drain  Gear  and  Relief  Valves  215 

viii. 


CONTENTS. 


4       Starting  Valves • 216 

5]     Reversing   Gear    217 

6]     Turning  Gear    220 

7]     Joints  and  Packing  220 

Reheaters    225 

9J     Governors  225 

[  10]     Counter  Gear    227 

fii]     Lagging 228 

[12]     Lubrication   and   Oiling   Gear    228 

25.  Piping 237 

[i]     Systems  and  Materials 237 

\2\     Expansion  Joint  239 

[3]     Globe  Angle  and  Straightway  Valves   240 

CHAPTER  V. 

Auxiliaries. 

26.  Circulating  Pumps '. 241 

27.  Condensers  243 

28.  Air  Pumps 245 

29.  Feed  Pumps  and  Injectors  251 

30.  Feed  Heaters 255 

31.  Filters 260 

32.  Evaporators  261 

33.  Direct  Acting  Pumps 263 

34.  Blowers  or  Fans 267 

35.  Separators 267 

36.  Ash  Ejectors  269 

37.  General  Arrangement  of  Machinery 271 

CHAPTER  VI. 

Operation,  Management  and  Repair. 

38.  Boiler*  Room  Routine 273 

[i]     Starting  Fires  and  Getting  Under  Way  273 

[2]     Fire  Room  Routine 277 

[3]     Emergencies  and  Casualties 287 

39.  Engine-Room  Routine  and  Management 298 

[i]     Getting  Under  Way 298 

[2]     Routine   Operation    301 

[3]     Minor  Emergencies  and  Troubles    304 

40.  Boiler  Corrosion 308 

41.  Boiler  Scale   319 

42.  Boiler  Overhauling  and  Repairs 328 

i  ]     Inspection  and  Test 328 

2]     Leakage  from  the  Joints  of  Boiler  Mountings 333 

'3]     Leakage  About  Shell  Joints 333 

4]     Leakage  at  Internal  Joints  334 

5]     Patches 336 

61     Cracks  and  Holes 336 

7       Blisters   and    Laminations    337 

8]     Tubes   338 

[9!     Leakage  About  Stays  and  Braces 339 

[10]  Bulging   or    Partial    Collapse   of    Furnace    or    Combustion 

Chamber  Plates 339 

FIT]     Split  in  Feed-Pipe 341 

43.  Engine  Overhauling,  Adjustment  and  Repairs  341 

i]     Cylinders  342 

2]     Pin  Joints  and   Bearings    343 

3]     Crosshead  Guides 345 

4]     Crosshead  Marks  346 


[12 


CONTENTS. 

PAGE. 

Lining  Up    347 

Valve  Gear 352 

Thrust    Bearings    353 

Circulating   Pump    353 

Condensers  353 

Air  Pumps   355 

Pumps  in  General  355 

Piping    355 


44.  Spare  Parts 356 

45.  Laying  Up  Marine  Machinery  356 

CHAPTER  VII. 

Valves  and  Valve  Gears. 

46.  Slide  Valves  358 

i]     Simple  Slide  Valve  358 

2]     Double  Ported  Slide  Valve 360 

3J     Piston  Valve   361 

4]     Equilibrium   Piston   365 

5]     J°y's  Assistant  Cylinder   366 

6]     Equilibrium    Rings    367 

_7]     Outside  and  Inside  Valves  368 

47.  Motion   Due   to    Simple   Excentric   and    Its    Representation   by 

Valve    Diagram 369 


[I] 
\2 


Simple  Excentric  369 

Oval  Valve  Diagram 372 


Bilgram   Valve    Diagram    377 

Zeuner  Valve  Diagram 379 

48.  Stephenson  Link  Valve  Gear 380 

49.  Braemme-Marshall  Gear 386 

50.  Joy  Valve  Gear   391 

51.  Walschaert  Valve  Gear  391 

52.  Crank  Valve  Gear  393 

53.  Details  of  Stephenson  Link  Valve  Gear   * 397 

fi]     Excentric  and  Strap  and  Excentric  Rod  397 

[2]     Link    400 

[3]     Link  Block  and  Valve  Stem  402 

54.  Valve  Setting 405 

i]     Putting  an  Engine  on  the  Center 405 

[2]     Setting  the  Valve 406 

[3]     Valve  Setting  from  the  Indicator  Card 408 


f: 


CHAPTER  VIII. 

Steam  Bngine  Indicators  and  Indicator  Cards. 

55.  Indicator  Cards 410 

[i]     Descriptive   410 

[2]     The  Indicator  Card  and  the  Operation  of  the  Valve  Gear.  .  413 

[3]     Working  up  Indicator  Cards  for  Power .  417 

[4]     Combined  Indicator  Cards 425 

56.  Steam  Engine  Indicators   429 

[i]     Descriptive 429 

[2]     Reducing  Motions  431 

[3]     Taking  an  Indicator  Card 434 

CHAPTER  IX. 

Special  Topics  and  Problems. 

57.  Heat  and  the  Formation  of  Steam 438 

[i]     Constitution  of  Matter   438 

[2]     Heat   439 

x. 


CONTENTS. 

SECTION*.  PAGE. 

[3]     Steam  ; 444 

[4]     Total  Heat  in  a  Substance  450 

[5]     Latent  Heat  in  Passing  from  Ice  to  Water 452 

58.  Steam  Boiler  Economy  453 

T  ]     General    Principles    453 

[2]     Evaporation  Per  Pound  of  Coal 455 

13]     Evaporation  Per  Pound  of  Combustible 459 

59.  Steam  Engine  Economy  460 

[i]     General    Principles    460 

[2]     Relation  of  Expansion  to  Economy 469 

[3]     Economy  of  the  Actual  Engine  471 

60.  Coal  Consumption  and  Related  Problems 472 

61.  The  Lever  Safety  Valve  and  the  Safety  Valve  Problem 476 

62.  The  Boiler  Brace  Problem   480 

63.  Strength  of  Boilers  485 

64.  Loss  by  Blow  Off 489 

65.  Gain  by  Feed  Water  Heating   491 

66.  The  Proportions  of  Cylinders  for  Multiple  Expansion  Engines.  .  492 

67.  Clearance  and  Its  Determination   494 

68.  The  Iiffect  of  Clearance  in  Modifying  the  Apparent  Expansion 

Ratio  as  Given  by  the  Point  of  Cut-Off   496 

69.  Engine   Constant    497 

70.  Indicated  Thrust 498 

71.  Reduced  Mean  Effective  Pressure   • 499 

72.  Pressure  on  Main  Guides  502 

73.  Force  Required  to  Move  a  Slide  Valve   503 

74.  Amount  of  Condensing  Water  Required  504 

75.  Work  Done  by  Pumos   505 

76.  Discharge  of  Steam  Through  an  Orifice 507 

77.  Computing  Weights  of  Parts  of  Machinery  508 

FT]     Units  to  be  Used   ". 508 

[2]     Approximations  and  Short   Cuts    509 

CHAPTER  X. 

Propulsion  and  Poweringf. 

78.  Measure  of  Speed  514 

79.  Propulsion 514 

80.  Screw  Propeller 517 

[i]     Definitions    517 

[2]     Varieties  of  Propellers 523 

[3!     Materials  526 

f4l     Measurement  of  Pitch   526 

81.  Paddle  Wheels    531 

82.  Powering  Ships 534 

83.  Reduction    of    Power   When   Towing   or   When   Vessel   is    Fast 

to  a  Dock 537 

84.  Trial  Trios   539 

85.  Special  Conditions  for  Speed  Trials   544 

CHAPTER  XI. 

Refrigeration. 

86.  General  Principles  545 

87.  Refrigeration  by  Freezing  Mixtures 546 

88.  Refrigeration  by  Vaporization  and  Expansion  547 

89.  Principal  Features  of  Ammonia  Refrigerating  Apparatus 549 

90.  Refrigeration  by  the  Expansion  of  a  Compressed  Gas   553 

91.  Principal  Features  of  Compressed  Air  Refrigerating  Apparatus  554 

92.  Operation  and  Care  of  Refrigerating  Machinery  556 

xi. 


CONTENTS. 


CHAPTER  XII. 


Electricity  on  Shipboard. 

SECTION.  PAGE. 

93.  Introductory 559 

94.  The  Dynamo  565 

95.  Wiring  and  The  Distribution  of  Light  and  Power  571 

96.  Lamps 575 

97.  Operation  and  Care  of  Electrical  Machinery  577 

i  ]     Routine  Care  577 

'2]     Faults 578 


Part  II. 


COMPUTATIONS  FOR  ENGINEERS. 

SECTION.  PAGE. 

1.  Common  Fractions  581 

i]     Units  of  Measurement  and  Definitions 581 

2]     Reduction  of  a  Mixed  Number  to  an  Improper  Fraction..  583 

3]     Reduction  of  an  Improper  Fraction  to  a   Mixed  Number  584 

4]     Reduction  of  Fractions  Without  Change  of  Value 584 

5]     Addition  of  Common  Fractions 586 

6]     Subtraction   of   Fractions    587 

7]     Multiplication  of  Fractions 588 

8]     Divisions  of  Fractions  588 

9]     Multiplication  and  Division  of  Fractions 589 

[10]     Complex  Fractions   591 

2.  Decimal  Fractions  592 

i  ]     Introductory    592 

2]     To  Reduce  Decimals  to  Lower  Terms  593 

3       To  Raise  Decimals  to  Higher  Terms 593 

4]     To  Reduce  a  Decimal  Fraction  to  a  Common  Fraction.  ..  .  593 
51     To  Reduce  a  Common  Fraction,  Proper  or  Improper,  to  a 

Decimal 593 

6]     To  Add  Decimals   594 

7]     To  Subtract  Decimals 594 

8]     To  Multiply  Together  Two  Numbers  Expressed  Decimally  595 
9]     To  Find  the  .Quotient  of  Two  Quantities,  Expressed  Deci- 
mally       595 

3.  Percentage   - 596 

4.  Compound   Numbers    599 

[ 1 1     Long  or   Linear   Measure    599 

'2]     AvoirdtiDois  Weight  or  Measure 599 

"3]     Square  Measure   599 

4]     Cubic  or  Volume  Measure 600 

"5]     Liquid   Measure    600 

6]     Dry  Measure  600 

7l     Shipping  Measure   600 

8]     The  Metric  System  of  Weights  and  Measures 600 

[9!     Conversion  Tables 601 

[iol     Reduction  of  Compound  Numbers    602 

fill     Addition  of  Compound  Numbers  603 

[12]     Subtraction  of  Compound  Numbers  603 

[13]     Multiplication  of  Compound  Numbers 604 

[14]     Division  of  Compound  Numbers 604 

5-     Duodecimals    605 

6.     Ratio   and   Proportion 607 

[i]     Simple  Proportion 607 


CONTENTS. 

SECTION*.  PAGE. 

[2]     Compound  Proportion  610 

7.  K\  oiution  and  Involution  612 

f i  ]     Introductory    612 

[2]  '  To  Extract  the  Square  Root 613 

[3]     To  Extract  the  Cube  Root  615 

8.  Mathematical  Signs,  Symbols  and  Operations 616 

9.  Geometry  and  Mensuration  621 

i  ]     Square    621 

2]     Rectangle    622 

3]     Parallelogram    622 

4]     Trapezoid    623 

5]     Triangle       623 

6       Right-Angled  Triangle    624 

7 j     Trapezium    625 

81     Regular  Polygons   625 

9]     Irregular  Figures 626 

10]     Circle    626 

1 1       Circular  Ring  or  Annulus 628 

12]     Sector  of  Circle 628 

13]     Segment  of  Circle   629 

14]     Ellipse 629 

15]     Figures  With  an  Irregular  Contour  630 

16]     Prism    633 

17]     Cylinder     634 

[18]  Any  Solid  with  a  Constant  Section  Parallel  to  the  Base, 

Either  Right  or  Oblique  635 

[19]     Wedge     635 

[20]     Right  Pyramid * 635 

\2i       General   Pyramid   636 

[22       Right  Circular  Cone  637 

[23       General  Cone 637 

[24]     Frustum  of  Right  Pyramid   '. .  638 

[25]     Frustum  of  General  Pyramid 639 

T26]     Frustum  of  Right  Cone 639 

[27]     Frustum  of  General  Cone   640 

[28]     Sphere    640 

[29!     Volume  of  Irregular   Shape    640 

[30  Volume  Generated  by  Any  Area  Revolving  About  an  Axis  641 

10.     Problems  in  Geometry 642 

[i]  At  Any  Point  in  a  Straight  Line  to  Erect  a  Perpendicular  642 

[2]     To  Bisect  the  Distance  Between  Two  Points   643 

[3]  To  Find  the  Center  from  which  to  Pass  an  Arc  of  Given 

Radius  Through  Two   Given  Points   643 

[4]  To  Divide  a  Given  Line  into  a  Given  Number  of  Equal 

Parts 643 

[5]  To  Construct  a  Triangle,  Having  Given  the  Three  Sides. ..  643 

[6]     To  Bisect  a  Given  Arc  or  Angle 644 

[7]     To  Construct  a  Mean  Proportional  644 

"[8]     To  Construct  a  Fourth  Proportional 644 

[9]  To    Construct   a    Square    Equivalent    in    Area   to   a    Given 

Rectangle    645 

[10]  To    Construct   a    Square    Equivalent   in    Area   to   a    Given 

Triangle     645 

TII]  With  One  Given  Side,  to  Construct  a  Rectangle  Equivalent 

to  a  Square   64; 

[12!     To  find  the  Length  of  an  Arc  of  a  Curve  645 

[13]     To  Construct  an  Ellipse  646 

[14]     To  Construct  any  Regular  Polygon    647 

[15]     To  Develop  the  Surface  of  a  Cylinder   648 


CONTENTS. 

'ION.  PAGE. 

[16]     To  Develop  the  Surface  of  a  Cylinder  which  is  Intersected 
by  Another  Cylinder,  the  Two  Axes  being  in  the  same 

Plane    648 

~i?]     To  Develop  the  Surface  of  a  Cone  t . . . .  649 

18]     To  Develop  the  Surface  of  the  Frustum  of  a  Cone 649 

[19]     To  Develop  the  Segments  of  an  Elbow  649 

11.  Physics    , 650 

i]     Acceleration  Due  to  Gravity 650 

2]     Specific  Gravity   650 

3],     Heat  Unit 651 

4]     Specific  Heat 651 

5]     Expansion   of   Metals    651 

12.  Mechanics     652 

1  Introductory 652 

2  Force    652 

3  Specification  of  a  Force   652 

4  Moment  of  a  Force 653 

5]     Resultant    653 

6]     Work    653 

7]     Power    653 

8]     Energy    655 

[9]  Conservation  of  Energy 656 

loj  Statics    656 

1 1  ]  Dynamics    656 

12]  Propositions  in   Statics   656 

13]  Mechanical  Powers  659 

14]  Examples  in  Mechanics 665 


\iv. 


Practical  Marine  Engineering 


CHAPTER  I. 

PRINCIPAL  MATERIALS  OF  ENGINEERING 
CONSTRUCTION. 

Sec.  i.    ALUMINUM. 

The  commercially  pure  metal,  i.  e.,  with  less  than  i  per  cent 
impurity,  is  white  in  color,  soft,  ductile  and  malleable.  It  melts 
at  about  1,160°  F.,  has  a  tensile  strength  of  about  15,000  Ib.  per 
square  inch  of  section,  but  lacks  in  stiffness  and  resilience,  or  the 
power  to  withstand  shocks. 

Aluminum  does  not  oxidize  readily  under  the  influence  of 
ordinary  air,  but  when  in  contact  with  sea  water,  or  in  air 
charged  with  sea  water,  the  corrosion  is  often  serious  in  extent. 
Aluminum  cannot  be  welded  except  electrically,  is  not  suitable 
for  forging  or  rolling  when  hot,  and  cannot  be  tempered  or  hard- 
ened. It  is,  however,  suitable  for  casting,  and  when  cold  can  be 
rolled  into  sheets  and  drawn  into  wire,  and  in  thin  sheets  or  small 
pieces  may  be  spun  or  flanged,  or  worked  under  the  hammer  in 
various  ways. 

Aluminum  unalloyed  is  of  comparatively  small  value  to  the 
engineer,  but  it  enters  into  several  valuable  alloys,  as  described 
in  Section  9,  and  its  use  in  this  way  has  increased  to  a  consider- 
able extent  within  the  past  few  years. 

Sec.  2.    ANTIMONY. 

The  pure  metal  is  whitish  in  color,  quite  brittle  and  crystal- 
line or  laminated  in  structure,  and  has  a  melting  point  of  about 
840°  F.  It  is  useless  in  the  pure  state  for  ordinary  engineering 
purposes,  but  is  a  valuable  ingredient  of  various  alloys  used  for 
bearing  metals,  etc.,  as  described  in  Section  9. 


2  PRACTICAL  MARINE  ENGINEERING. 

Sec.  3.    BISMUTH. 

The  pure  metal  is  light  red  in  color,  very  brittle  and  highly 
crystalline  in  structure,  with  a  melting  point  of  about  510°  F.  It 
is  useless  in  the  pure  state  for  engineering  purposes,  but  forms  a 
part  of  various  alloys  used  for  bearing  metals,  etc.,  as  described 
in  Section  9. 

Sec.  4.    COPPER. 

In  the  pure  state  the  metal  is  red  in  color,  soft,  ductile  and 
malleable,  with  a  melting  point  of  about  2,000°  F.,  and  a  tensile 
strength  of  from  20,000  to  30,000  Ib.  per  square  inch  of  section. 
Copper  is  not  readily  welded  except  electrically,  but,  on  the 
other  hand,  is  readily  joined  by  the  operation  of  brazing.  At- 
tempts have  been  made  to  temper  or  harden  it,  but  the  operation 
has  not  been  made  a  practical  success.  It  is  readily  forged  and 
cast,  and  when  cold  may  be  rolled  into  sheets  or  drawn  into  wire, 
and  in  sheets  or  small  pieces  may  be  spun  or  flanged  or  worked 
under  the  hammer  in  various  ways. 

The  tensile  strength  of  copper,  rapidly  falls  off  as  the  tem- 
perature rises  above  about  400°  F.,  so  that  at  from  800°  to  900°  the 
strength  is  only  about  one-half  what  it  is  at  ordinary  tempera- 
tures. This  peculiarity  of  copper  should  be  borne  in  mind  when 
it  is  used  in  places  where  the  temperature  is  liable  to  rise  to  these 
figures.  Again,  if  copper  is  raised  nearly  to  its  melting  point  in 
contact  with  the  air  it  readily  unites  with  oxygen  and  loses  its 
strength  in  large  degree,  becoming,  when  cool,  crumbly  and  brit- 
tle. Copper  in  this  condition  is  said  to  have  been  burned.  The 
possibility  of  thus  injuring  the  tenacity  of  copper  is  of  the  highest 
importance  in  connection  with  the  use  of  brazed  joints  in  steam 
pipes. 

In  the  operation  of  brazing  a  joint,  the  surfaces  to  be  joined 
are  cleaned,  bound  together  with  wire  or  otherwise,  then  sup- 
plied with  brazing  solder  in  small  bits,  mixed  with  borax  as  a 
flux,  and  placed  in  a  clear  fire  until  the  solder  melts  and  forms 
the  joint.  The  brazing  solder,  or  hard  solder,  as  it  is  often  called, 
is  usually  a  brass  or  alloy  of  copper  and  zinc.  The  melting  point 
of  all  such  alloys  is  below  that  of  copper,  and  when  copper  is 
joined  to  brass,  or  two  pieces  of  brass  are  joined  together,  the 
solder  used  must  have  a  melting  point  lower  than  either  of  these 
metals.  In  the  operation  of  brazing  a  copper  joint,  therefore,  the 
greatest  care  must  be  taken  in  the  selection  of  a  solder  and  in 
attention  to  the  fire,  so  that  there  may  be  no  danger  of  burning 


MATERIALS.  3 

the  copper,  and  thus  endangering  the  quality  of  the  metal  in  the 
joint. 

Copper  unalloyed  is  used  chiefly  for  pipes  and  fittings,  espe- 
cially for  junctions,  elbows,  bends,  etc.  For  large  sizes  the  ma- 
terial is  made  in  sheets,  bent  and  formed  to  the  desired  shape  and 
brazed  at  the  seams.  Small  sizes  are  either  made  by  the  same 
general  process  or  from  solid  drawn  pipe,  which  may  be  bent  as 
desired  after  drawing.  Copper  is  also  largely  used  as  the  chief 
ingredient  of  the  various  brasses  and  bronzes,  as  described  in 
Section  9. 

Sec.  5.    IRON  AND  STEEI,. 

Classification. 

It  will  be  convenient  to  give  here  a  general  classification  of 
iron  and  steel  products  based  on  the  methods  of  manufacture. 
The  following  is  the  classification  used  by  Prof.  J.  B.  Johnson  in 
his  text  book  on  the  Materials  of  Construction. 

MALLEABLE. 

Wrought  Iron. — Rolled  or  forged  from  a  puddle  ball ;  it  con- 
tains slag  and  other  impurities  and  cannot  be  hardened  by  sud- 
den cooling. 

Steel. — Rolled  or  forged  from  a  cast  ingot  and  free  from  slag 
and  similar  matter. 

Soft  Steel. — Will  weld  (with  care),  and  cannot  be  hardened 
by  sudden  cooling.  It  is  sometimes  called  ingot  iron,  and  has  the 
same  uses  as  wrought  iron. 

Medium  Steel. — Welds  imperfectly  except  by  electricity. 
Will  not  harden  by  sudden  cooling. 

Hard  Steel. — Will  not  weld.  Hardens  by  sudden  cooling. 
Tool  steel,  etc. 

SEMI-MALLEABLE. 

Steel  Castings. — Malleable  metal  cast  into  forms. 
Malleable  Cast  Iron. — Non-malleable  metal  cast  into  forms 
and  then  brought  to  a  semi-malleable  condition. 

NON-MALLEABLE. 

Cast  Iron ;  Hard  Cast  Steel. — Non-malleable  metal  cast  into 
forms. 

In  describing  these  products  at  length  we  shall  find  it  con- 
venient to  begin  with  cast  iron. 


4  PRACTICAL  MARINE  ENGINEERING. 

[i]  Cast  Iron. 

This  material  consists  of  a  mixture  and  combination  of  iron 
and  carbon,  with  other  substances  in  varying  proportions. 

(i)  Influence  of  Carbon.  In  the  molten  condition  the  car- 
bon is  dissolved  by  the  iron  and  held  in  solution  just  as  ordin- 
ary salt  is  dissolved  by  water.  The  mixture  or  combination  of 
the  two  elements  is  thus  entirely  uniform.  The  proportion  of 
carbon  which  pure  melted  iron  can  thus  dissolve  and  hold  in 
solution  is  about  3^  per  cent.  If  chromium  or  manganese  is 
present  also,  the  capacity  for  carbon  is  much  increased,  while 
with  silicon,  on  the  other  hand,  the  capacity  for  carbon  is  de- 
creased. In  the  various  grades  of  cast  iron  the  proportion  of 
carbon  is  usually  found  between  2  per  cent  and  4.5  per  cent. 

Now,  when  such  a  molten  mixture  cools  and  becomes  solid, 
there  is  a  tendency  for  a  part  of  the  carbon  to  be  separated  out 
and  no  longer  remain  in  intimate  combination  with  the  iron. 
The  carbon  thus  separated  or  precipitated  out  from  the  iron 
takes  that  form  known  as  graphite,  and  collects  together  in  very 
small  flakes  or  scales.  The  carbon  which  remains  in  intimate 
combination  with  the  iron  is  said  to  be  combined,  while  that 
which  is  separated  out  is  usually  called  graphitic. 

The  qualities  of  cast  iron  depend  chiefly  on  the  proportion 
of  total  carbon  and  on  the  relative  proportions  of  combined  and 
graphitic  carbon. 

With  a  high  proportion  of  graphitic  carbon  the  iron  is  soft 
and  tough,  with  low  tensile  strength,  and  breaks  with  a  coarse 
grained  dark  or  grayish  colored  fracture.  In  fact  the  substance 
in  this  condition  may  be  considered  as  nearly  pure  iron  with  fine 
flakes  of  graphite  entangled  and  distributed  through  it,  thus  giv- 
ing to  the  iron  a  spongy  structure.  The  iron  thus  forms  a  kind 
of  continuous  mesh  about  the  graphite,  which  decreases  the 
strength  by  reason  of  the  decrease  of  cross-sectional  area 
actually  occupied  by  the  iron  itself.  Such  irons  are  termed  gray. 

As  the  relative  proportion  of  graphitic  carbon  decreases 
and  that  of  combined  carbon  increases,  the  iron  takes  on  new 
properties,  becoming  harder  and  more  brittle.  Its  tensile 
strength  also  increases  to  a  certain  extent,  and  the  fracture  be- 
comes fine  grained  or  smooth  and  whiter  in  color.  When  these 
characteristics  are  pronounced  the  iron  is  said  to  be  white. 
When  about  half  the  carbon  is  combined  and  half  separates  out 
as  graphite,  the  effect  is  to  produce  a  distribution  of  dark  spots 


MATERIALS.  5 

or  points  scattered  over  a  whitish  field.  Such  irons  are  said  to 
be  mottled. 

In  a  general  way  with  a  large  proportion  of  total  carbon 
there  is  likely  to  be  formed  a  considerable  amount  of  graphitic 
carbon,  and  hence  such  irons  are  usually  gray  and  soft.  With 
a  large  proportion  of  carbon  also  the  iron  melts  more  readily  and 
its  fluidity  is  more  pronounced.  As  the  proportion  of  total  car- 
bon decreases  the  cast  iron  approaches  gradually  the  condition 
of  steel,  whose  properties  will  be  discussed  in  a  later  paragraph. 

Of  the  special  ingredients  in  cast  iron  the. combined  carbon 
is  one  of  greatest  importance.  It  is  that  chiefly  which  by  uniting 
with  the  iron  gives  it  new  qualities,  and  the  principal  influence 
of  other  substances  lies  in  the  effect  which  they  may  have  on  the 
proportion  of  this  ingredient.  As  between  graphitic  and  com- 
bined carbon,  the  former  does  not  affect  the  quality  of  the  iron 
itself,  but  acts  physically  by  affecting  the  structure  of  the  cast- 
ing; while  the  latter,  by  entering  into  combination  with  the 
iron,  acts  chemically  and  produces  a  new  substance  with  different 
qualities.  The  following  percentages  of  combined  carbon  are 
recommended  for  qualities  of  iron  as  indicated: 

PROPORTION  OF  COMBINED  CARBON. 

Soft  cast  iron 10  to  .  15  of  one  per  cent. 

Greatest  tensile  strength about  .45  of  one  per  cent. 

Greatest  transverse  strength about .  70  of  one  per  cent. 

Greatest  crushing  strength one  per  cent  or  over. 

The  proportions  of  combined  and  graphitic  carbon  are  in- 
fluenced by  the  rate  of  cooling,  and  by  the  presence  or  absence 
of  various  other  ingredients.  Slow  cooling  allows  time  for  the 
separation  of  the  carbon  and  thus  tends  to  form  graphitic  car- 
bon and  soft  gray  irons.  Quick  cooling,  or  chilling  in  the  ex- 
treme case,  prevents  the  formation  of  graphitic  carbon  and  thus 
tends  to  form  hard,  white  irons. 

In  addition  to  carbon,  small  quantities  of  silicon,  sulphur, 
phosphorus,  manganese  and  chromium  may  be  found  in  cast  iron. 

(2)  Influence  of  Silicon.  The  fundamental  influences  of 
silicon  are  two.  (a)  It  tends  to  expel  the  carbon  from  the  com- 
bined state  and  thus  to  decrease  the  relative  proportion  of  com- 
bined carbon  and  increase  that  of  graphitic  carbon.  (b)  Of 
itself  silicon  tends  to  harden  cast  iron  and  to  make  it  brittle. 

These  two  influences  are  opposite  in  character,  since  an  in- 
crease in  graphitic  carbon  softens  the  iron.  In  usual  cases  the 


6  PRACTICAL  MARINE  ENGINEERING. 

net  result  is  a  softening  of  the  iron,  an  increase  in  fluidity,  and 
a  general  change  toward  those  qualities  possessed  by  iron  with 
a  high  proportion  of  graphitic  carbon.  This  applies  with  a  pro- 
portion of  silicon  from  2  per  cent  to  4  per  cent.  With 
more  than  this  the  influence  on  the  carbon  is  but  slight  and  the 
result  on  the  iron  is  to  decrease  the  strength  and  toughness, 
giving  a  hard  but  brittle  and  weak  grade  of  iron. 

A  chilled  cast  iron  is  an  iron  which  if  cooled  slowly  would 
be  gray  and  soft,  but,  as  explained  in  (i),  by  sudden  cooling, 
from  contact  with  a  metal  mould  or  other  means,  becomes  white 
and  hard,  especially  at  and  near  the  surface.  Certain  grades 
of  cast  iron  tend  to  chill  when  cast  in  sand  moulds.  This  prop- 
erty is  usually  undesirable.  In  such  cases  the  tendency  can  be 
prevented  by  the  addition  of  silicon,  which,  by  forcing  the  car- 
bon into  the  graphitic  state  on  cooling,  prevents  the  formation 
of  the  hard,  chilled  surface.  In  all  cases  the  actual  effect  of 
adding  silicon  will  depend  much  on  the  character  of  the  iron 
used  as  a  base,  and  only  a  statement  of  the  general  tendencies 
can  here  be  given. 

To  sum  up,  a  white  iron  which  would  give  hard,  brittle  and 
porous  castings  can  be  made  solid,  softer  and  tougher  by  the  ad- 
dition of  silicon  to  the  extent  of  perhaps  2  or  3  per  cent.  As  the 
silicon  is  increased  the  iron  will  become  softer  and  grayer  and 
the  tensile  strength  will  decrease.  At  the  same  time  the  shrink- 
age will  decrease,  at  least  for  a  time,  though  it  may  increase 
again  with  large  excess  of  silicon.  The  softening  and  toughen- 
ing influence,  however,  will  only  continue  so  long  as  additional 
graphite  is  formed,  and  when  most  of  the  carbon  is  brought  into 
this  state  the  maximum  effect,  has  been  produced,  and  any  fur- 
ther addition  of  silicon  will  decrease  both  strength  and  tough- 
ness. 

(3)  Influence  of  Sulphur.  Authorities  are  not  in  entire 
agreement  as  to  the  influence  of  sulphur  on  cast  iron,  some  be- 
lieving that  it  tends  to  increase  the  proportion  of  combined  car- 
bon, while  others  maintain  that  it  tends  to  decrease  both  the 
combined  carbon  and  silicon.  It  is  generally  agreed,  however, 
that  in  proportions  greater  than  about  .15  to  .20  of  I  per  cent  it 
increases  the  shrinkage  and  the  tendency  to  chill,  and  decreases 
the  strength.  Sulphur  does  not,  however,  readily  enter  cast 
iron  under  ordinary  conditions,  and  its  influence  is  not  especially 
feared.  An  increase  in  the  proportion  of  sulphur  in  cast  iron 


MATERIALS.  7 

is  most  likely  to  result  from  an  absorption  of  sulphur  in  the 
coke  during  the  operation  of  melting  in  the  cupola. 

(4)  Influence   of   Manganese.     This    element   by   itself   de- 
creases fluidity,  increases  shrinkage,  and  makes  the  iron  harder 
and  more  brittle.      It  combines  with  iron  in  all  proportions. 
With  manganese  less  than  one-half,  the  combination  is  usually 
called  spicgcleifcn.      With  manganese  more  than  one-half  it  is 
called  ferro-manganese.      One  of  the  most  important  properties 
of  manganese  in  combination  with  iron  is  that  it  increases  the 
capacity  of  the  iron  for  carbon.     Pure  iron  will  only  take  about 
3*X  per  cent  of  carbon,  while  with  the  addition  of  manganese 
the  proportion  may  rise  to  6  per  cent  or  7  per  cent.     Manganese 
is  also  believed  to  decrease  the  capacity  of  iron  for  sulphur,  and 
to  this  extent  may  be  a  desirable  ingredient  in  proportions  not 
exceeding  I  per  cent  to  il/2  per  cent. 

(5)  Influence  of  Chromium.     This  substance  is  rarely  found 
in  cast  iron,  but  it  has  the  property,  when  present  in  large 
proportion,  of  raising  the  capacity  of  the  iron  for  carbon  from 
about  $y2  per  cent  up  to  about  12  per  cent. 

(6)  Shrinkage  of  Cast  Iron.     At  the  moment  of  hardening, 
cast  iron  expands  and  takes  a  good  impression  of  the  mould. 
In  the  gradual  cooling  after  setting,  however,  the  metal  con- 
tracts, so  that  on  the  whole  there  is  a  shrinkage  of  about  %  in. 
per  foot  in  all  directions,  though  this  amount  varies  somewhat 
with  the  quality  of  the  iron  and  with  the  form  and  dimensions 
of  the  pattern.      In  a  general  way  hardness  and  shrinkage  in- 
crease and  decrease  together. 

(7)  Strength  and  Hardness  of  Cast  Iron.     The  hardness  of 
cast  iron  is  chiefly  dependent  'on  the  amount  of  combined  car- 
bon, as  noted  above  in  (i). 

The  strength  is  also  chiefly  dependent  on  the  same  ingre- 
dient. As  shown  in  (i),  the  greatest  crushing  strength  is  ob- 
tained with  sufficient  combined  carbon  to  make  a  rather  hard, 
white  iron,  while  for  the  maximum  transverse  or  bending 
strength  the  combined  carbon  is  somewhat  less  and  the  iron 
only  moderately  hard,  and  for  the  greatest  tensile  strength  the 
combined  carbon  is  still  less  and  the  iron  rather  soft.  Metal 
still  softer  than  this  grade  works  with  the  greatest  facility,  but 
is  deficient  in  strength. 

Numerical  values  for  the  strength  will  be  given  at  a  later 
point. 


8  PRACTICAL  MARINE  ENGINEERING. 

(8)  Uses  of  Cast  Iron  in  Marine  Engineering.     Cast  iron  is 
used  for  cylinders,  cylinder  heads,  liners,   slide  valves,  valve 
chests  and  connections,  and  generally  for  all  parts  having  con- 
siderable complexity  of  form.     It  is  also  used  for  columns,  bed 
plates,  bearing  pedestals,  caps,  etc.,  though  cast  and  forged  steel 
are  to  some  extent  displacing  cast  iron  for  some  of  these  items. 
It  is  also  used  for  grate  bars,  furnace  door  frames,  and  minor 
boiler  fittings,  and  for  a  great  variety  of  special  purposes  usually 
connected  with  the  stationary  or  supporting  parts  of  machines. 

(9)  Inspection  of  Castings.     In  the  inspection  of  castings 
care  must  be  had  to  note  the  texture  of  the  surface,  and  to  this 
end  the  outer  scale  and  burnt  sand  should  be  carefully  removed 
by  the  use  of  brushes  or  chipping  hammer,  or,  if  necessary, 
by  pickling     in  dilute   muriatic   acid.     The*  flaws    most   liable 
to  occur  are  blow  holes   and   shrinkage   cracks.      The   latter, 
however,    are    not    often   met   with    when    the    moulding   and 
casting  are  properly  carried  out.     The  parts  of  the  casting  most 
liable  to  be  affected  by  blow  holes  are  those  on  the  upper  side 
or  near  the  top.     On  this  account  a  sinking  head  or  extra  piece 
is  often  cast  on  top,  into  which  the  gases  and  impurities  may 
collect.      This  is  afterward  cut  off,  leaving  the  sounder  metal 
below. 

The  presence  of  blow  holes,  if  large  in  size  or  in  great 
number  and  near  the  surface,  may  often  be  determined  by  tap- 
ping with  a  hand  hammer.  The  sound  given  out  will  serve  to 
indicate  to  an  experienced  ear  the  probable  character  of  the 
metal  underneath. 

(10)  Special  Operations  on  Cast  Iron.     Cast  iron  may  be 
softened  and  toughened  by  the  process  of  malleablizing,  as  de- 
scribed in  (2).      It  may  be  somewhat  hardened  on  the  surface 
by  arresting  the  usual  process  of  malleablizing  at  a  suitable 
point  and  then  hardening  as  for  steel.     This  operation  arrested 
before  completion  results  in  the  formation  of  a  surface  layer  of 
material  having  essentially  the  properties  of  steel. 

Cast  iron  may  be  brazed  to  itself  or  to  most  of  the  com- 
mon structural  metals  by  the  use  of  a  brazing  solder  of  suitable 
melting  point,  and  with  proper  care  in  the  operation.  Cast 
iron  may  also  be  united  to  itself  or  to  wrought  iron  or  steel  by 
the  operation  of  burning.  This  consists  in  placing  in  position  the 
two  pieces  to  be  united,  and  then  allowing  a  stream  of  melted 
cast  iron  to  flow  over  the  surfaces  to  be  joined,  the  adjacent 


MATERIALS.  9 

parts  being  protected  by  fire  clay  or  other  suitable  material. 
The  result  is  to  soften  or  partially  melt  the  surfaces  of  the 
pieces,  and  by  arresting  the  operation  at  the  right  moment  they 
may  be  securely  joined  together. 

[a]  Malleable  Iron. 

(i)  Composition  and  Manufacture.  If  a  casting  of  hard, 
white  iron,  or  one  with  a  large  proportion  of  combined  carbon, 
be  packed  in  some  material  which  will  not  fuse  at  a  red  heat, 
which  will  exclude  the  air,  support  the  piece  and  prevent  defor- 
mation when  hot,  and  if  it  be  then  subjected  to  continuous  red 
heat  for  some  days,  the  combined  carbon  will  be  separated  from 
the  iron,  but  will  not  be  able  to  collect  together  in  flakes  or 
scales  or  to  form  the  same  structure  as  in  soft,  gray  cast  iron. 
In  consequence  the  iron  crystals  remain  in  more  intimate  con- 
tact, much  as  in  steel,  and  the  tensile  strength  and  toughness 
are  greatly  increased. 

It  has  long  been  supposed  that  this  operation  involved  an 
actual  withdrawal  of  the  carbon  from  the  iron,  and  to  this  end 
the  substances  usually  employed  are  either  the  common  red  oxide 
of  iron  in  the  form  of  hematite  iron  ore,  or  the  black  oxide  in 
the  form  of  mill  scale,  or  the  corresponding  oxide  of  manganese. 
These  have  a  decarbonizing  effect ;  that  is,  under  the  conditions 
existing  they  will  to  some  extent  withdraw  the  carbon  from  the 
surface  layer  of  iron.  Analyses  of  malleable  iron  show,  how- 
ever, that  only  to  a  slight  extent  is  Ihe  carbon  actually  with- 
drawn as  a  whole,  and  that  the  principal  change  is  in  the  condi- 
tion of  the  carbon,  as  above  explained.  The  surface  effect, 
however,  extending  in,  as  it  does,  for  perhaps  1-16  in.,  is  un- 
doubtedly a  valuable  feature,  and  while  a  good  quality  of  malle- 
able iron  has  been  made  by  the  use  of  river  sand  as  a  packing 
medium,  the  use  of  the  substances  mentioned  above  is  rather  to 
be  preferred. 

In  order  that  the  process  may  be  successful,  the  iron  must 
have  nearly  all  the  carbon  in  the  combined  state,  and  must  be 
low  in  sulphur,  as  the  latter  substance  is  found  to  greatly  in- 
crease the  time  necessary.  It  has  been  customary  to  use  only 
good  charcoal-melted  iron  in  which  the  sulphur  is  very  low, 
though  a  coke-melted  iron  is  quite  as  suitable,  provided  the  pro- 
portion of  sulphur  is  correspondingly  small.  The  process  can 
rarely  be  applied  to  very  large  castings,  because  such,  cooling 


io  PRACTICAL  MARINE  ENGINEERING. 

slowly,    usually    show    a    considerable    proportion    of    graphitic 
carbon. 

To  carry  out  the  process  the  castings  are  embedded  in  the 
material  selected.  The  whole  is  then  inclosed  in  a  cast-iron  box 
or  pot  and  is  subjected  to  a  full  red  heat  for  from  two  or  three 
days  to  as  many  weeks,  depending  on  the  size  of  the  piece. 

(2)  Physical   and   Mechanical   Properties.     Outside    of    the 
numerical  information,  to  be  given  later,  attention  may  be  called 
to  the  ductility  of  malleable  iron,  which  is  from  four  to  six  times 
that  of  cast  iron,  though  only  about  one-tenth  that  of  wrought 
iron.     Nevertheless  good  malleable  iron  can  be  bent  and  twisted 
to  a  very  considerable  extent  before'  breaking,  and  its  ability  to 
withstand  blows  or  shocks  is  very  much  greater  than  cast  iron. 
Malleable  iron  may  with  care  be  forged  and  welded,  and  it  may 
be  case  hardened  much  as  with  wrought  iron. 

(3)  Uses  in  Marine  Engineering.      Malleable  iron  is  used 
for  junction  boxes  and  for  pipe  fittings  in  certain  varieties  of 
water-tube  boilers,  and  to  some  extent  for  general  pipe  fittings 
on  board  ship.      It  would  seem  that  the  use  of  this  material 
might  with  advantage  be  extended  to  many  parts  in  which  more 
strength  and  toughness  are  required  than  can  be  provided  by 
cast  iron  of  the  ordinary  type. 


[3]  Wrought  Iron. 

(i)  Composition  and  Manufacture.  Wrought  iron  is  nearly 
pure  iron  mixed  with  more  or  less  slag.  Nearly  all  the  wrought 
iron  used  in  modern  times  is  made  by  the  puddling  process.  For 
the  details  of  this  process  reference  may  be  had  to  text-books 
on  metallurgy.  We  can  only  note  here  that  in  a  furnace  some- 
what similar  to  the  open-hearth  referred  to  in  [5]  (4)  most  of  the 
carbon,  silicon  and  other  special  ingredients  of  cast  iron  are  re- 
moved by  the  combined  action  of  the  flame  and  of  a  molten  bath 
of  slag  or  fluxing  material  consisting  chiefly  of  black  oxide  of 
iron.  As  this  process  approaches  completion  small  bits  of  near- 
ly pure  iron  begin  to  separate  out  from  the  bath  of  melted  slag 
and  unite  together.  This  is  helped  along  by  the  puddling  bar,  and 
after  the  iron  has  thus  become  separated  from  the  liquid  slag 
it  is  taken  out,  hammered  or  squeezed,  and  rolled  down  into  bars 
or  plates.  Some  of  the  slag  is  necessarily  retained  in  the  iron 
and  by  the  process  of  manufacture  is  drawn  out  into  fine  threads, 


MATERIALS.  11 

giving  to  the  iron  a  stringy  or  fibrous  appearance  when  nicked 
and  bent  over  or  when  pulled  apart. 

The  proportion  of  carbon  in  wrought  iron  is  very  small, 
ranging  from  .02  to  .20  of  one  per  cent.  In  addition,  small 
amounts  of  sulphur,  phosphorus,  silicon  and  manganese  are 
usually  present. 

The  proportion  of  sulphur  should  not  exceed  .01  of  one 
per  cent.  Excess  of  sulphur  makes  the  iron  red-short,  that  is, 
brittle  when  red  hot.  ' 

The  proportion  of  phosphorus  may  vary  from  .05  to  .25  of 
one  per  cent.  Excess  of  phosphorus  makes  the  metal  cold- 
short, that  is,  brittle  when  cold. 

The  proportion  of  silicon  may  vary  from  .05  to  .30  of  one 
per  cent. 

The  proportion  of  manganese  may  vary  from  .005  to  .05  of 
one  per  cent.  The  influence  of  the  silicon  and  manganese  is 
usually  slight  and  unimportant. 

(2)  Special   Properties.     Wrought    iron    is    malleable    and 
ductile,  and  may  be  rolled,  forged,  flanged  and  welded.      It  can- 
not be  hardened  as  steel,  though  by  the  process-  of  case-harden- 
ing a  surface  layer  of  steel  is  formed  and  may  be  hardened. 
Wrought  iron  may  be  welded,  because  for  a  considerable  range 
of  temperature  below  melting  (which  takes  place  only  at  a  very 
high  temperature  indeed)  the  iron  becomes  soft  and  plastic,  and 
two  pieces  pressed  together  in  this  condition  unite  and  form  on 
cooling  a  junction  nearly  as  strong  as  the  solid  metal.    In  order 
to  be  thus  successful,  however,  the  iron  must  be  heated  sufficient- 
lytobringit  to  the  plastic  condition,  yet  not  overheated,  and  there 
must  be  employed  a  flux  (usually  borax)  which  will  unite  with 
the  iron  oxide  and  other  impurities  at  the  joint,  and  form  a  thin 
liquid  slag,  which  may  be  readily  pressed  out  in  the  operation, 
thus  allowing  the  clean  metal  faces  of  the  iron  to  effect  a  union 
as  desired. 

(3)  Uses  in  Marine  Engineering.     In  modern  practice  the 
place  of  wrought  iron  in  marine  engineering  has  been  almost  en- 
tirely taken  by  steel.     Its  former  office  was  for  all  moving  parts 
requiring  strength  and  toughness.      It  is  still  used  to  some  ex- 
tent for  the  stay  bolts  and  braces  of  boilers,  and  for  boiler  tubes. 

[4]  Blisters  and  I/aminations. 

With  modern  boiler  material  these  defects  are  happily  rare. 


12  PRACTICAL  MARINE  ENGINEERING. 

In  older  practice,  however,  when  wrought  iron  was  the  material 
employed  for  boiler  plates,  such  defects  were  quite  frequently 
met  with.  A  lamination  consisted  in  the  separation  of  the  ma- 
terial of  the  plate  into  layers  not  welded  together  and  therefore 
lacking  the  strength  and  solidity  of  the  plate  proper.  The  for- 
mation of  such  places  was  usually  due  to  the  presence  of  slag  in 
the  iron  which  in  the  operation  of  rolling  the  plates  would  be- 
come thinned  out  into  a  sheet  or  layer  .separating  the  two  gaits 
of  the  iron  and  preventing  them  from  becoming  welded  together 
and  thus  forming  a  solid  homogeneous  plate.  Such  places  may 
vary  in  size  from  a  trifling  amount  up  to  patches  of  several 
square  feet  in  area.  Now  when  a  plate  with  such  laminations  is 
worked  into  the  structure  of  a  boiler  with  the  continual  fluctua- 
tions of  temperature  and  the  consequent  expansions  and  con- 
tractions, it  very  frequently  happens  that  the  two  parts  of  the 
laminations  become  separated  from  each  other,  and  in  particular 
the  thinner  of  the  two  will  become  raised  often  to  a  considerable 
extent,  thus  forming  a  so-called  blister.  The  chief  danger  from 
such  a  blister  on  the  heating  surface  arises  from  the  non-con- 
ductivity of  the  plate  for  heat  at  this  point,  and  the  consequent 
danger  of  its  overheating  and  giving  rise  to  a  serious  rupture. 
Further  reference  to  this  point  will  be  found  in  Sec.  38  [3]. 

In  examining  a  plate  for  laminations  or  small  blisters  not 
plainly  shown  to  the  eye,  the  hammer  test  is  usually  considered 
the  most  reliable.  The  plate  is  tapped  over  its  surface,  and 
judging  by  the  sound  an  experienced  ear  can  usually  detect  the 
locality  and  approximate  extent  of  trouble  of  this  character. 

[5]  Steel. 

(i)  General  Composition.  The  properties  of  steel  depend 
partly  on  the  proportions  of  carbon  and  other  ingredients  which 
it  may  contain,  and  partly  on  the  process  of  manufacture.  The 
proportion  of  carbon  is  intermediate  between  that  for  wrought 
iron  and  for  cast  iron.  In  the  so-called  mild  or  structural  steel 
the  carbon  is  usually  from  i-io  to  1-4  or  1-3  of  one  per  cent. 
In  spring  steel  the  carbon  proportion  is  somewhat  greater,  and 
in  high  carbon  grades  such  as  are  used  for  tool  steel,  etc.,  the 
carbon  is  from  .6  to  1.2  per  cent.  In  addition  to  the  carbon 
there  may  be  sulphur,  phosphorus,  silicon  and  manganese  in 
varying  but  very  small  amounts. 

From  the  proportion  of  carbon  it  follows  that  steel  may  be 


MATERIALS.  13 

made  either  by  increasing  the  proportion  in  wrought  iron  or 
decreasing  the  proportion  in  cast  iron.  The  earlier  processes 
followed  the  first  method,  and  high-grade  steels  are  still  made 
in  this  way  by  the  crucible  process. 

(2)  Crucible    Steel.     In    this    process    a    pure    grade    of 
wrought  iron  is  rolled  out  into  flat  bars.      These  are  then  cut 
and  piled  and  packed  with  intermediate  layers  of  charcoal  and 
subjected  to  a  high  temperature  for  several  days.     This  recar- 
bonizes  or  adds  carbon  to  the  wrrought  iron,  and  thus  makes 
what  is  then  called  cement  or  blister  steel.     These  bars,  are  then 
broken  into  pieces  of  convenient  size,  placed  in  small  crucibles, 
melted,  and  cast  into  bars  or  into  such  forms  as  are  desired. 

NOTE. — Mild  or  structural  steel  is  made  wholly  by  the  second  general 
method— the  reduction  of  the  proportion  of  carbon  in  cast  iron.  There  are 
two  general  processes,  known  as  the  Bessemer  and  the  Siemens  Martin  or 
Open-hearth. 

(3)  Bessemer  Process.     In  this  process  the  carbon  and  sili- 
con are  burned  almost  entirely  out  of  the  cast  iron  by  forcing 
an  air  blast  through  the  molten  iron  in  a  vessel  known  as  a  con- 
verter.   A  small  amount  of  Spiegel  eisen  or  iron  rich  in  carbon  and 
manganese  is  then  added  in  such  weight  as  to  make  the  propor- 
tion of  carbon  and   manganese   suitable   for  the   charge   as   a 
whole.     The  steel  thus  formed  is  then  cast  into  ingots  or  into 
such  forms  as  may  be.  desired. 

In  this  process  no  sulphur  or  phosphorus  is  removed,  so 
that  it  is  necessary  to  use  a  cast  iron  very  nearly  free  from  these 
ingredients  in  order  that  the  steel  may  have  the  properties  de- 
sired. A  modification  by  means  of  which  the  phosphorus  is  re- 
moved, and  known  as  the  basic  Bessemer  process,  is  used  to 
some  extent.  In  this,  calcined  or  burnt  lime  is  added  to  the 
charge  just  before  pouring.  This  unites  with  the  phosphorus, 
removes  it  from  the  steel,  and  brings  it  into  the  slag.  In  the 
basic  process  the  lining  of  the  converter  is  made  of  gannister  or 
a  calcined  magnesia  limestone,  in  order  that  it  may  not  also  be 
attacked  by  the  added  limestone  and  the  resulting  slag. 

In  that  form  of  Bessemer  process  first  noted,  and  often 
known  as  the  acid  process  in  distinction  from  the  latter  or  basic 
process,  the  lining  of  the  converter  is  of  ordinary  fire  clay  or 
like  material. 

The  removal  of  the  phosphorus  by  the  basic  process  makes 
possible  the  use  of  an  inferior  grade  of  cast  iron.  At  the  same 


i4  PRACTICAL  MARINE  ENGINEERING. 

time,  engineers  are  not  altogether  agreed  as  to  the  relative 
values  of  the  two  products,  and  many  prefer  steel  made  by  the 
acid  process  from  an  iron  nearly  free  from  phosphorus  at  the 
start. 

(4)  The  Open-hearth  Process.     In  this  process  a  charge  of 
material  consisting  of  wrought  iron,  cast  iron,  steel  scrap,  and 
sometimes  certain  ores,  is  melted  on  the  hearth  of  a  reverbera- 
tory  furnace  heated  by  gas  fuel  on  the  Siemens  Martin  or  re- 
generative system.     The  carbon  is  thus  partially  burned  out  in 
much  the  same  manner  as  for  wrought  iron,  and  the  proportion 
of  carbon  is  brought  down  to  the  desired  point  or  slightly  be- 
low.     A  charge  of  Spiegel  eisen  or  ferro-manganese  is  then 
added  in  order  that  the  manganese  may  act  on  any  oxide  of  iron 
slag  which  remains  in  the  bath,  and  which  would  make  the  steel 
red-short  if  allowed  to  form  a  part  of  the  charge.    The  mangan- 
ese separates  the  iron  out  from  the  oxide,  returns  it  to  the  bath, 
while  the  carbon  joins  in  with  that  already  present,  and  thus 
produces  the  desired  proportions. 

Here  as  with  the  similar  operation  with  the  Bessemer  con- 
verter there  is  no  removal  of  either  sulphur  or  phosphorus,  and 
only  materials  nearly  free  from  these  ingredients  can  be  used 
for  steel  of  satisfactory  quality.  With  very  low  carbon,  how- 
ever, a  little  phosphorus  seems  to  be  desirable  to  add  strength 
to  the  metal.  This  limitation  of  the  available  materials  has  led, 
as  with  the  Bessemer  process,  to  the  use  of  calcined  limestone, 
which  unites  with  most  of  the  phosphorus  and  holds  it  in  the 
slag.  Here,  as  in  the  Bessemer  process  also,  it  is  necessary  to 
use  a  basic  lining  for  the  furnace,  and  it  is  known  as  the  basic 
open-hearth  process.  By  distinction  the  method  without  the 
use  of  the  limestone  has  come  to  be  known  as  the  acid  open- 
hearth  process. 

As  between  the  products  of  these  two  kinds  of  open-hearth 
process,  there  is  much  difference  of  opinion  among  engineers. 
Either  will  produce  good  steel  with  proper  care,  and  neither  will 
without  it.  It  is  usually  considered  sufficient  to  specify  the  al- 
lowable limits  for  the  proportions  of  phosphorus  and  sulphur 
and  leave  the  choice  of  the  acid  or  basic  processes  to  the  maker. 

(5)  Open-hearth    and    Bessemer    Steels    Compared.       Open- 
hearth  steel  is  usually  preferred  for  structural  material  in  mar- 
ine engineering.      This  is  because  : 

(a)     It  seems  to  be  more  reliable  and  less  subject  to  un- 


MATERIALS.  15 

expected  or  tmexplainable  failure  than  the  Bessemer  product. 

(b)  Analysis  shows  that  it  is  much  more  homogeneous  in 
composition  than  Bessemer  steel,  and  experience  shows  that  it 
is  much  more  uniform  in  physical  quality.      This  is  due  to  the 
process   of  manufacture,  which  is   much  more  favorable  to  a 
thorough  mixing  of  the  charge  than  in  the  Bessemer  process. 

(c)  The  open-hearth  steel  may  be  tested  from  time  to  time 
during  the  operation,  so  that  its  composition  may  be  determined 
and  adjusted  to  fulfil  specified  conditions.     This  is  not  possible 
with  the  Bessemer  process,  and  the  latter  product  is  therefore 
not  under  so  good  control  as  is  the  open-hearth. 

(6)  Influence  of  Sulphur  on   Steel.      Sulphur   makes   steel 
red-short  or  brittle  when  hot,  and  interferes  with  its  forging  and 
welding  properties.     Manganese  tends  to  counteract  the  bad  ef- 
fects of  sulphur.      Good  crucible  steel  has  rarely  more  than  .01 
of  one  per  cent.      In  structural  steel  the  proportion  may  vary 
from  .02  to  .08  or  .10  of  one  per  cent.     When  possible  it  should 
be  reduced  to  not  more  than  .03  or  .04  of  one  per  cent. 

(7)  Influence  of  Phosphorus  on  Steel.     Phosphorus  increases 
the  tensile  strength  and  raises  the  elastic  limit  of  low  carbon 
or    structural    steel,   but   at   the   expense    of   its    ductility   and 
toughness  or  ability  to  withstand  shocks  and  irregularly  applied 
loads.     It  is  thus  considered  as  a  dangerous  ingredient,  and  the 
amount  allowable  should  be  carefully  specified.     This  is  usually 
placed  from  .02  to  .10  of  one  per  cent. 

(8)  Influence  of  Silicon  on  Steel.     Silicon  tends  to  increase 
the  tensile  strength  and  to  reduce  the  ductility  of  steel.      It  also 
increases  the  soundness  of  ingots  and  castings,  and  by  reducing 
the  iron  oxide  tends  to  prevent  red-shortness.     The  process  of 
manufacture  usually  removes  nearly  all  of  the  silicon,  so  that  it 
is  not  an  element  likely  to  give  trouble  to  the  steel  maker.     The 
proportion  allowed  should  not  be  more  than  from  .10  to  .20  of 
one  per  cent. 

(9)  Influence  of  Manganese  on  Steel.      This  element  is  be- 
lieved to  increase  hardness  and  fluidity,  and  to  raise  the  elastic 
limit  and  increase  the  tensile  strength.      It  also  removes  iron 
oxide  and  sulphur,  and  tends  to  counteract  the  influence  of  such 
amounts  of  sulphur  and  phosphorus  as  may  remain.      It  is  thus 
an  important  factor  in  preventing  red-shortness.      The  propor- 
tion needed  to  obtain  these  valuable  effects  is  usually  found  be- 
tween .20  and  .50  of  one  per  cent. 


16  PRACTICAL  MARINE  ENGINEERING. 

(10)  Semi-steel.  A  metal  bearing  this  trade  name  has  in 
recent  years  attracted  favorable  attention  among  engineers  and 
has  come  into  considerable  use  where  somewhat  greater 
strength  and  toughness  are  required  than  can  be  provided  by 
cast  iron. 

Semi-steel  is  made  by  melting  up  mild  steel  scrap,  such  as 
punchings  and  clippings  of  boiler  plate,  with  cast  iron  pig,  in  the 
proportion  of  about  25  or  30  per  cent  of  the  former  to  75  or  70 
per  cent  of  the  latter.  The  presence  of  manganese  and  other 
special  fluxes  in  small  proportions  is  also  found  to  add  essen- 
tially to  the  strength,  toughness  and  good  machining  qualities 
of  the  product.  In  this  way  is  obtained  a  material  having  a 
tensile  strength  of  35,000  Ib.  or  over,  and  a  toughness  and  ability 
to  withstand  shocks  decidedly  greater  than  for  cast  iron,  and 
with  fairly  good  machining  qualities.  Semi-steel  casts  as  read- 
ily as  most  grades  of  cast  iron,  and  its  shrinkage  and  genera! 
manipulation  are  about  the  same.  The  chief  drawback  seems 
to  lie  in  the  danger  of  hardness  under  the  lathe,  planer  or  bor- 
ing tool,  but  with  the  proper  mixtures  this  is  avoided,  .and  a 
material  very  satisfactory  for  many  purposes  in  marine  engi- 
neering is  thus  produced. 

(n)  Mechanical  Properties  of  Steel.  The  tensile  strength 
of  the  lowest  carbon  steel,  say  about  .10  of  one  per  cent  carbon, 
is  usually  not  above  from  50,000  to  55,000  Ib.  per  square  inch  of 
section.  The  strength  increases  with  the  increase  of  carbon, 
and  with  not  above  the  usual  proportions  o£  sulphur  and  phos- 
phorus, quite  uniformly.  Experiment  shows  that  under  these 
circumstances  the  strength  will  increase  up  to  75,000  Ib.  per 
square  inch,  or  higher,  at  the  rate  of  from  1,200  to  1,500  Ib.  per 
.01  of  one  per  cent  of  carbon  added.  At  the  same  time,  with 
the  increase  in  strength  the  ductility  decreases,  so  that  a  proper 
choice  must  be  made  according  to  the  particular  uses  for  which 
the  steel  is  intended.  With  the  best  grades  of  tool  steel  with 
carbon  ranging  from  y2  to  i  per  cent  and  over,  the  strength 
ranges  from  80,000  Ib.  upward  to  120,000  Ib.,  and  even  higher 
in  exceptional  cases. 

Flange  and  rivet  steel  must  be  tough  and  ductile  in  the  high- 
est degree.  Such  steel  has  usually  a  tensile  strength  between 
50,000  and  60,000  Ib.  and  an  elastic  limit  of  30,000  to  40,000  Ib. 
Its  elongation  in  8  in.  is  from  30  to  35  per  cent,  and  reduction  of 
area  at  the  ruptured  section  from  50  to  60  per  cent.  It  will 


MATERIALS.  17 

bend  cold  ort  itself  and  close  down  flat  under  hammer  or  press, 
up  to  a  thickness  of  1/4  in.  to  I  in.  without  a  sign  of  fracture. 

Shell  steel,  used  for  boiler  shells,  etc.,  has  usually  a  strength 
between  55,000  and  65,000  Ib. ;  elastic  limit  from  33,000  to  45,- 
ooo  Ib. ;  elongation  in  8  in.  of  25  to  30  per  cent,  and  reduction  of 
area  of  50  to  60  per  cent. 

For  shafting  the  quality  of  the  steel  is  about  the  same  as 
for  shell  plates.  For  piston  and  connecting  rods  the  strength 
is  rather  higher,  and  ductility  somewhat  lower. 

For  steel  castings  the  strength  required  is  usually  from  60,- 
ooo  to  65,000  Ib.,  with  an  elongation  in  8  in.  of  from  10  to  15 
per  cent. 

(12)     Various  Specifications  for  Structural  Steel. 

U.  S.  Navy. 

COMPOSITION    OF    BOILER    PLATES. 

Phosphorus :  Not  over  .035  of  one  per  cent. 
Sulphur :   Not  over  .040  of  one  per  cent. 

STRENGTH  OF  SHELL  PLATES. 

Tensile  Strength:  Between  65,000  and  73,000  Ib.  per  square 
inch. 

Elongation  (transverse) :   Not  less  than  22  per  cent  in  8  in. 

Elongation  (longitudinal) :  Not  less  than  25  per  cent  in  8  in. 

Elastic  Limit :   Not  less  than  35,000  Ib.  per  square  inch. 

Cold  Bending  Test. — One  piece  cut  from  each  shell  and 
curved  head  plate,  as  finished  at  the  rolls  for  cold-bending  test, 
must  bend  over  flat  on  itself  without  sign  of  fracture. 

STRENGTH    OF    FURNACE    AND    FLANGE    PLATES. 

Tensile  Strength :  Between  52,000  and  60,000  Ib.  per  square 
inch. 

Elongation :   Not  less  than  26  per  cent  in  8  in. 

Quenching  Test. — One  piece  shall  be  cut  from  each  furnace 
or  flange  plate  as  finished  at  the  rolls  for  quenching  test,  and 
after  heating  to  a  dark  cherry  red  plunged  into  water  at  a  tem- 
perature of  82  deg.  F.  The  piece  thus  prepared  must  be  bent 
double  round  a  curve  of  which  the  diameter  is  not  more  than  the 
thickness  of  the  piece  tested,  without  showing  any  cracks.  The 
ends  of  the  pieces  must  be  parallel  after  bending. 


i8  PRACTICAL  MARINE  ENGINEERING. 

BOILER    RIVETS. 

Kind  of  Material. — Steel  for  boiler  rivets  must  be  made  by 
the  open-hearth  process  and  must  not  show  more  than  .035  of 
one  per  cent  of  phosphorus,  nor  more  than  .04  of  one  per  cent 
of  sulphur,  and  must  be  of  the  best  composition  in  other  re- 
spects. 

Tensile  Tests. — These  specimens  for  rivets  for  use  in  the 
longitudinal  seams  of  boiler  shells  shall  have  from  62,000  to 
70,000  Ib.  per  square  inch  tensile  strength,  with  an  elongation 
of  not  less  than  25  per  cent  in  8  in. ;  and  all  others  shall  have  a 
tensile  strength  of  from  54,000  to  62,000  Ib.  per  square  inch, 
with  an  elongation  of  not  less  than  28  per  cent  in  8  in. 

Shearing  Tests. — From  each  heat,  rivets  must  show  a  shear- 
ing strength  of  at  least  51,000  Ib.  per  square  inch  for  rivets  to  be 
used  in  longitudinal  seams  of  boiler  shells,  and  at  least  44,000 
Ib.  per  square  inch  for  all  other  boiler  rivets.  Rivets  to  be 
driven  at  the  same  heat  used  for  working. 

Hammer  Test. — From  each  lot  six  rivets  are  to  be  taken  at 
random  and  submitted  to  the  following  tests : 

(a)  Two  rivets  to  be  flattened  out  cold  under  the  hammer 
to  a  thickness  of  one-half  the  diameter  of  the  part  flattened  with- 
out showing  cracks  or  flaws. 

(b)  Two  rivets  to  be  flattened  out  hot  under  the  hammer 
to  a  thickness  of  one-third  the  diameter  of  the  part  flattened 
without  showing  cracks  or  flaws — the  heat  to  be  the  working 
heat  when  driven. 

(c)  Two  rivets  to  be  bent  cold  into  the  form  of  a  hook 
with  parallel  sides  without  showing  cracks  or  flaws. 

RODS,  SHAPES  AND  FORCINGS  FOR  BOILER  BRACING. 

Kind  of  Material. — Steel  for  stay  rods  and  braces  must  be 
made  by  the  open-hearth  process,  and  must  not  show  more  than 
.035  of  one  per  cent  of  phosphorus,  nor  more  than  .04  of  one 
per  cent  of  sulphur,  and  must  be  of  the  best  composition  in 
other  respects. 

Treatment. — All  material  for  boiler  bracing  must  be  an- 
nealed after  working. 

Tensile  Test. — Bracing  coming  into  contact  with  the  fire 
must  have  a  tensile  strength  of  from  50,000  to  58,000  Ib.,  and  an 
elongation  of  not  less  than  28  per  cent  in  8  in.,  or  of  33  per 
cent  in  2  in.  in  case  8-in.  specimens  can  not  be  secured.  Other 


MATERIALS.  19 

bracing  must  have  a  tensile  strength  of  not  less  than  65,000  lb., 
and  an  elongation  of  not  less  than  24  per  cent  in  8  in.,  or  of  30 
per  cent  in  2  in.  in  case  8-in.  specimens  can  not  be  secured. 

Bending  Test. — One  bar  l/2  in.  thick,  cut  from  each  lot  of 
the  bracing  coming  in  contact  with  the  fire,  must  stand  bending 
double  to  an  inner  diameter  of  i  in.  after  quenching  in  water  at 
a  temperature  of  82  deg.  F.,  from  a  dark  cherry-red  heat  with- 
out showing  cracks  or  flaws.  A  similar  piece  cut  from  each  lot 
of  the  other  bracing  must  stand  cold  bending  double  to  an  inner 
diameter  of  i  in.  without  showing  cracks  or  flaws. 

Opening  and  Closing  Tests. — Angles,  T  bars,  etc.,  are  to  be 

subjected  to  the  following  additional  tests :    A  piece  cut  from 

one  bar  in  twenty  to  be  opened  out  flat  while  cold ;   a  piece  cut 

from  another  bar  in  the  same  lot  shall  be  closed  down  on  itself 

until  the  two  sides  touch  without  showing  cracks  or  flaws. 

CONNECTING    AND    PISTON    RODS    AND    VALVE    STEMS. 

Tensile  Strength :   Not  less  than  80,000  lb.  per  square  inch. 

Elongation :   Not  less  than  26  per  cent  in  2  in. 

Elastic  Limit :   Not  less  than  50,000  lb.  per  square  inch. 

Bending  Test. — One  longitudinal  bar  y2  in.  thick,  cut  from 
each  forging,  must  stand  bending  double,  when  cold,  to  an  in- 
ner diameter  of  i  in.  without  showing  cracks  or  flaws. 

THRUST    LINE    AND    PROPELLER    SHAFTING. 

Tensile  Strength :   Not  less  than  80,000  lb.  per  square  inch. 

Elongation :   Not  less  than  25  per  cent  in  2  in. 

Elastic  Limit :   Not  less  than  50,000  lb.  per  square  inch. 

CRANK    SHAFTS. 

Tensile  Strength :   Not  less  than  58,000  lb.  per  square  inch. 

Elongation :    Not  less  than  30  per  cent  in  2  in. 

Bending  Test. — Bars  y2  in.  thick,  cut  from  each  length  of 
shaft,  must  stand  bending  double  to  an  inner  diameter  of  i  in. 
without  showing  cracks  or  flaws. 

STEEL    CASTINGS. 

Phosphorus  :   Not  more  than  .06  of  one  per  cent. 
Tensile  Strength:   Not  less  than  60,000  lb.  per  square  inch. 
Elongation  (for  moving  parts):    Not  less  than  15  per  cent 
in  8  in. 


20  PRACTICAL  MARINE  ENGINEERING. 

Elongation  (other  castings) :  Not  less  than  10  per  cent  in 
8  in. 

Bending  Test. — A  bar  I  in.  square  shall  bend  cold  without 
showing  cracks  or  flaws,  through  an  angle  of  120  deg.  for  cast- 
ings for  moving  parts  of  machinery,  and  90  deg.  for  other  cast- 
ing, over  a  radius  not  greater  than  il/2  in. 


U.  S.  Inspection  Requirements  for  Boiler  Plate. 

Phosphorus :   Not  more  than  .06  of  one  per  cent. 

Sulphur :   Not  more  than  .04  of  one  per  cent. 

Elongation  (J4  m-  and  under)  :  25  per  cent  in  2  in. 

Elongation  (l/4  in.  to  7-16  in.  inc.) :   25  per  cent  in  4  in. 

Elongation  (7-16  in.  to  I  in.  inc.)  :  25  per  cent  in  8  in. 

Elongation  (i  in.  and  over) :  25  per  cent  in  6  in. 

Reduction  of  Area  at  Rupture  (y2  in.  and  under) :  Not  less 
than  50  per  cent. 

Reduction  of  Area  at  Rupture  (l/2  in.  to  34  in.) :  Not  less 
than  45  per  cent. 

Reduction  of  Area  at  Rupture  (fy  in.  and  over) :  Not  less 
than  40  per  cent. 

American  Boilermakers*  Association  Requirements. 

Phosphorus  :   Not  over  .04  per  cent. 

Sulphur :   Not  over  .03  per  cent. 

Tensile  Strength :  55,000  to  65,000  Ib. 

Elongation  (3/£  in.  and  under) :  20  per  cent  in  8  in. 

Elongation  (3/£  in.  to  3/^  in.) :  22  per  cent  in  8  in. 

Elongation  (34  in.  and  over) :   25  per  cent  in  8  in. 

Cold  Bending. — For  plates  y2  in.  thick  and  under,  specimen 
must  bend  back  on  itself  without  fracture.  For  plates  over  y2 
in.  thick,  specimen  must  bend  180  deg.  around  a  mandril  one 
and  one-half  times  thickness  of  plate  without  fracture. 


British  Board  of  Trade  Requirements. 

Tensile  Strength  of  Plates  Not  Exposed  to  Flame :  60,480 
to  71,680  Ib.  per  square  in. 

Tensile  Strength  of  Plates  Exposed  to  Flame :  58,240  to 
67,200  Ib.  per  square  inch. 

Elongation:    From  18  to  25  per  cent  in  10  in. 


MATERIALS.  21 

Standard  Specifications  Adopted  by  the  Association  of  Ameri- 
can Steel  Manufacturers. 

Special  Open-hearth  Plate  and  Rivet  Steel. 

Steel  shall  be  of  four  grades,  as  follows :  Extra  Soft,  Fire- 
box, Flange  or  Boiler,  and  Boiler  Rivet  Steel. 

Extra  Soft,  Fire-box  and  Boiler  Rivet  Steel:  Maximum 
phosphorus,  .04  per  cent ;  maximum  sulphur,  .04  per  cent. 

Flange  or  Boiler  Steel :  Maximum  phosphorus,  .06  per 
cent ;  maximum  sulphur,  .04  per  cent. 

PHYSICAL    PROPERTIES. 

Extra  Soft  and  Boiler  Rivet  Steel. 

Ultimate  Strength :  45,000  to  55,000  Ib.  per  square  inch. 
Elastic  Limit :  Not  less  than  one-half  the  ultimate  strength. 
Elongation :   28  per  cent. 

Cold  and  Quench  Test :  Bends  180  deg.  flat  on  itself  with- 
out fracture  on  outside  of  bent  portion. 

Fire-box  Steel. 

Ultimate  Strength :   52,000  to  62,000  Ib.  per  square  inch. 
Elastic  Limit :  Not  less  than  one-half  the  ultimate  strength. 
Elongation  :  26  per  cent. 

Cold  and  Quench  Test :  Bends  180  deg.  flat  on  itself  with- 
out fracture  on  outside  of  bent  portion. 

Flange  or  Boiler  Steel. 

Ultimate  Strength :   52,000  to  62,000  Ib.  per  square  inch. 

Elastic  Limit :  Not  less  than  one-half  the  ultimate  strength. 

Elongation  :   25  per  cent. 

Cold  and  Quench  Test:  Bends  180  deg.  flat  on  itself  with- 
out fracture  on  outside  of  bent  portion. 

(13)  Special  Properties  of  Steel.  Mild  or  low  carbon  steel 
may  be  welded,  forged,  flanged,  rolled  and  cast.  It  can  not  be 
tempered  or  hardened  with  a  proportion  of  carbon  lower  than 
about  24  °f  one  Per  cent.  High  carbon  steel  can  be  welded 
only  imperfectly  and  if  very  high  in  carbon  not  at  all.  It  can 
be  forged  with  care,  and  cast  into  forms  as  desired.  It  can  be 
tempered  or  hardened  by  heating  to  a  full  yellow  and  quenching 
in  cold  water  or  by  other  means,  and  then  drawing  the  temper 
to  the  point  desired. 

Mild  steel  should  not  be  worked  under  the  hammer  or 
flanging  press  at  a  low  or  "blue"  heat,  as  such  working  is  found 


22  PRACTICAL  MARINE  ENGINEERING. 

in  many  cases  to  leave  the  metal  brittle  and  unreliable.  Steel 
in  order  to  weld  satisfactorily  should  have  a  low  proportion  of 
sulphur,  and  special  care  is  required  in  the  operation,  because 
the  range  of  temperature  through  which  the  metal  is  plastic  and 
fit  for  welding  is  less  than  with  wrought  iron. 

In  the  operation  of  tempering,  the  steel  after  quenching  is 
very  hard  and  brittle.  In  order  to  give  to  the  metal  the  prop- 
erties desired,  the  temper  is  drawn  down  by  heating  it  up  to  a 
certain  temperature,  and  then  quenching  again,  or,  better  still, 
allowing  it  to  cool  gradually,  provided  the  temperature  does  not 
rise  above  the  limiting  value  suitable  for  the  purpose  desired. 
If  the  reheating  is  done  in  a  bath  of  oil  the  conditions  may  be 
kept  under  good  control  and  the  final  cooling  may  be  slow.  If 
the  reheating  is  in  or  over  a  fire  the  control  is  lacking  and  the 
piece  must  be  quenched  as  soon  as  the  proper  temperature  is 
reached.  This  is  usually  determined  by  the  cplor  of  the  oxide 
or  scale  which  forms  on  a  brightened  surface  of  the  metal.  The 
following  table  shows  the  temperatures,  corresponding  colors, 
and  uses  for  which  the  various  tempers  are  suited : 

445o°°    S±$l™:}     Hardest  and  keenest  cutting  tool, 

470°  Full  yellow.  )      Cutting  tools  requiring  less  hardness 

490°  Brown  yellow  or  orange,  f  and  more  toughness. 

510°  Purplish.  )      Tools  for  working  softer  materials,  or  those  required 

530°  Purple,     f  to  stand  rough  usage. 

550°  Light  blue.  ]      Spring  temper.      Used  for  tools  requiring  great 

560°  Full  blue.     [•  elasticity  or  toughness,  or  for  working  very   soft 

6ooc  Dark:  blue.  J  materials. 

(14)  Special  Steels.  In  the  common  grades  of  steel  the 
valuable  properties  are  due  to  the  presence  of  carbon  modified 
in  some  degree  by  other  ingredients  as  already  described. 
There  are  other  substances  which  by  uniting  with  iron  in  small 
proportions  are  able  to  give  to  the  combination  increased 
strength  or  hardness  or  other  valuable  properties.  We  have 
thus  various  special  steels  in  which  the  properties  may  be  due 
to  the  presence  of  both  carbon  and  other  ingredients,  or  due 
chiefly  to  special  ingredients  other  than  carbon.  Of  these 
special  steels  we  may  note  the  following : 

Nickel  steel,  containing  somewhere  about  3  per  cent  of 
nickel  and  varying  amounts  of  carbon,  is  found  to  have  in- 
creased strength  and  toughness  as  compared  with  ordinary 
steel.  Nickel  steel  is  most  extensively  used  for  armor  plate, 


MATERIALS.  23 

though  to  some  extent  it  has  been  employed  in  Government 
work  for  screw-shafts  and  for  boiler  plates.  For  the  former 
purposes  it  has  given  excellent  satisfaction,  but  for  the  latter 
use  difficulty  has  been  met  with  in  obtaining  plates  free  from 
surface  defects. 

Chrome  steel,  containing  from  .5  to  1.5  or  2  per  cent  of 
chromium  may  be  made  excessively  hard,  but  it  is  not  always 
reliable,  and  is  not  regarded  with  general  favor. 

Tungsten  steel  or  mushet  steel  is  a  steel  containing  carbon 
and  tungsten,  the  latter  in  proportions  as  high  as  8  to  10  per  cent. 
This  steel  must  be  forged  with  .care  and  is  excessively  hard. 
The  hardness  is  not  increased  by  tempering,  but  is  naturally 
acquired  as  the  metal  cools.  Hence  it  is  said  to  be  self-harden- 
ing. Some  specimens  contain  also  small  amounts  of  mangan- 
ese and  silver.  Its  chief  use  is  for  lathe  and  planer  or  other 
cutting  and  shearing  tools  where  excessive  hardness  is  required. 

(15)  Uses  of  Steel  in  Marine  Construction.  In  modern 
practice  mild  or  structural  steel  is  used  entirely  in  the  con- 
struction of  ships. 

The  same  general  class  of  material  is  used  for  all  parts  of 
boilers,  though  the  tubes  are  still  sometimes  made  of  wrought 
iron. 

Cast  steel  is  used  for  various  parts  of  engines  such  as  pis- 
tons, crosshead  blocks,  columns,  bed-plates,  bearing  pedestals 
and  caps,  propeller  blades,  and  for  many  small  pieces  and  fit- 
tings. Pistons  are  made  almost  exclusively  of  cast  steel.  For 
most  of  the  other  items  mentioned  cast  iron  is  still  used,  prob- 
ably to  a  larger  extent  than  cast  steel,  especially  where  the  cast- 
ings are  large  and  complicated  in  form,  as  with  columns  and 
bed-plates. 

Forged,  steel  is  used  for  columns,  piston-rods,  connecting- 
rods,  crank  and  line  shafting,  and  for  many  other  smaller  and 
minor  parts. 

Sec.  6.  I,EAD. 

Lead  is  a  very  soft,  dense  metal,  grayish  in  color  after  ex- 
posure to  the  air,  but  of  a  bright  silvery  luster  when  freshly  cut. 
Commercial  lead  often  contains  small  amounts  of  iron,  copper, 
silver  and  antimony,  making  it  harder  than  the  pure  metal.  It 
is  very  malleable  and  plastic.  In  engineering,  lead  is  chiefly 
of  value  as  an  ingredient  of  bearing  metals  and  other  special  al- 
loys. Lead  piping  is  also  used  to  some  extent  for  water  sue- 


24  PRACTICAL  MARINE  ENGINEERING. 

tion  and  delivery  pipes  where  the  pressure  is  only  moderate,  and 
where  the  readiness  with  which  it  may  be  bent  and  fitted  adapts 
it  for  use  in  contracted  places. 

Sec.  7.    TIN. 

Tin  is  a  soft,  white,  lustrous  metal  with  great  malleability. 
Commercial  tin  usually  contains  small  portions  of  many  other 
substances,  such  as  lead,  iron,  copper,  arsenic,  antimony  and 
bismuth.  It  is  largely  used  as  an  alloy  in  the  various  bronzes 
and  other  special  metals.  Tin  resists  corrosion  well  and  in  con- 
sequence is  often  used  as  a  coating  for  condenser  tubes.  It  is 
also  used  for  coating  iron  plates,  the  product  being  the  so- 
called  "tin  plate"  of  commerce.  It  melts  at  about  450  deg., 
which  corresponds  to  a  steam  pressure  of  about  400  Ibs.  per 
square  inch.  Due  to  this  low  melting  point  tin  is  often  used  as 
the  composition  for  safety  plugs  in  boilers. 

Sec.  8.    3INC. 

Zinc,  or  "spelter,"  as  it  is  often  called  commercially,  is  a 
brittle  and  moderately  hard  white  metal  with  a  very  crystalline 
fracture.  The  impurities  most  commonly  found  in  zinc  are  iron, 
lead  and  arsenic.  It  is  used  chiefly  as  an  alloy  in  the  various 
brasses,  bronzes,  etc.,  and  as  a  coating  for  iron  and  steel  plates, 
rods,  etc.  The  process  of  applying  zinc  for  such  a  coating  is 
called  "galvanizing,"  and  the  product  "galvanized"  iron  or  steel. 
Electricity,  however,  is  not  used  in  the  process,  the  articles, 
after  being  well  cleaned,  being  simply  dipped  in  a  tank  of  melted 
zinc  and  then  withdrawn.  Slabs  of  zinc  are  also  used  in  marine 
boilers  to  prevent  corrosion. 

Sec.  9.    AI,I,OYS. 

A  mixture  of  two  or  more  metals  is  called  anta//0;y.  The 
properties  of  an  alloy  are  often  surprisingly  different  from  those 
of  its  ingredients.  The  melting  point  is  sometimes  lower  than 
that  of  any  of  the  ingredients,  while  the  strength,  elastic  limit 
and  hardness  are  often  higher  than  for  any  of  them. 

Mixtures  of  copper  and  zinc  are  called  brass.  Mixtures  of 
copper  and  tin,  or  copper,  tin  and  zinc,  with  sometimes  other  sub- 
stances in  small  proportion,  form  gun  metals,  compositions  and 
bronzes.  These  terms  are,  however,  rather  loosely  employed. 
Various  mixtures  of  two  or  more  of  the  metals — copper,  tin,  zinc, 
lead,  antimony — form  the  various  bearing  metals. 


MATERIALS.  25 

Brass  and  composition  are  used  for  piping  and  pipe-fitting; 
globe,  gate,  check  and  safety  valves  ;  condenser  tubes  and  shells  ; 
sleeves  for  tail  shafts,  and  for  a  great  number  of  small  fittings 
and  attachments  for  which  the  metal  may  be  suited.  The 
bronzes  are  employed  for  many  of  the  uses  of  brass  where  more 
hardness,  strength  or  rigidity  are  required.  They  are  used  with 
especial  success  as  a  material  for  propeller  blades. 

The  white  metals,  supported  or  backed  by  some  other 
metal,  such  as  brass,  cast  iron  or  cast  steel,  to  give  the  neces- 
sary strength,  are  now  very  largely  used  for  bearing  surfaces. 

PROPORTIONS  OF  INGREDIENTS  FOR  VARIOUS  ALLOYS. 

In  the  following  proportions  the  numbers  after  the  ingred- 
ients denote  the  number  of  parts  in  100  of  the  mixture.  They 
represent  either  the  usual  proportions,  or  the  results  of  special 
analyses  of  samples,  and  have  been  collected  from  various 
sources.  The  alloys  are  arranged  in  the  alphabetical  order  of 
their  names  to  facilitate  ready  reference : 

Admiralty  Bronze. — Copper  87,  tin  8,  zinc  5. 

Aluminum  Brass. — Copper  63,  zinc  34,  aluminum  3. 

Aluminum  Bronze. — Copper  89  to  98,  aluminum  n  to  2. 

Anti-Friction,  A. — Zinc  i,  iron  .65,  lead  78.75,  antimony 
19.6. 

Anti-Friction,  B. — Copper  1.6,  tin  98.13,  iron  trace. 

Anti-Friction,  C. — Copper  3.8,  tin  78.4,  lead  6,  antimony 
1 1.8. 

Babbitt  (Light'}. — Copper  1.8,  tin  89.3,  antimony  8.9. 

Babbitt  (Heavy). — Copper  3.7,  tin  88.9,  antimony  7.4. 

Brass,  Common  Yellow. —  Copper  65.3,  zinc  32.7,  lead  2. 

Brazing  Metal. — Copper  84,  zinc  16. 

Brazing  Solder. — Copper  50,  zinc  50. 

Bush  Metal. — Copper  80,  tin  5,  zinc'  10,  lead  5. 

Delta  Metal. — Copper  50  to  60,  tin  I  to  2,  zinc  34  to  44,  iron 
2  to  4. 

Deoxidized  Bronze. — Copper  82,  tin  12.46,  zinc  3,23,  iron  .10, 
lead  2.14,  phosphorus  trace,  silver  .07. 

Gun  Metal. — Copper  89,  tin  8.25,  zinc  2.75. 

Magnolia. — Tin  ?,  zinc  trace,  iron  trace,  lead  83.55,  anti- 
mony 16.45. 

Manganese  Bronze. — Copper  88.64,  tin  8.7,  zinc  1.57,  iron 
.72,  lead  .30. 


26  PRACTICAL  MARINE  ENGINEERING. 

Muntz  Metal. — Copper  60,  zinc  40. 

Navy  Brass. — Copper  62,  tin  i,  zinc  37. 

Navy  Composition. — Copper  88,  tin  10,  zinc  2. 

Navy  Journal  Boxes. — Copper  82.8,  tin  13.8,  zinc  3.4. 

Parsons  White  Metal. — Copper  1.68,  tin  72.9,  zinc  22.9,  lead 
1.68,  antimony  .84. 

Phosphor  Bronze. — Copper  90  to  92,  phosphide  of  tin  10  to  8. 

Steam  Metal. — Copper  85,  tin  6.5,  zinc  4.5,  lead  4.25. 

Tobin  Bronze. — Copper  59  to  61,  tin  i  to  2,  zinc  37  to  38, 
iron  .1  to  .2,  antimony  .30  to  .35. 

White  Metal. — Lead  88,  antimony  12. 

Sec.  10.    THE  TESTING   OF  METALS. 

[i]  Different  Kinds  of  Tests. 

Metals  may  be  tested  for  strength  in  various  ways — in  ten- 
sion, by  pulling  apart  a  test  piece  of  specified  pattern  and  size  ;  in 
compression,  by  crushing  a  piece  of  suitable  dimensions ;  in  cross 
breaking,  by  supporting  a  bar  at  two  points  and  breaking  or 
bending  it  in  the  testing  machine  by  a  load  applied  at  an  inter- 
mediate point;  in  torsion,  by  twisting  apart  a  bar  in  a  machine 
especially  designed  for  the  purpose ;  in  direct  shearing,  by  break- 
ing a  riveted  or  pin  joint  connection  in  the  usual  machine;  for 
impact  or  shock,  by  letting  a  weight  drop  through  a  certain 
height  and  by  its  blow  develop  suddenly  the  stress  in  the  ma- 
terial. 

[a]  Explanation  of  Terms  Used. 

Ultimate  Strength. — The  ultimate  strength,  of  a  test  piece  is 
the  load  required  to  produce  fracture,  reduced  to  a  square  inch 
of  original  section;  or  in  other  words,  the  ultimate  or  highest 
load  divided  by  the  original  area.  Thus  if  the  area  of  the 
cross-section  of  a  test  piece  is  .42  sq.  in.  and  the  load  producing 
fracture  is  28,400  Ib. ,  the  ultimate  strength  equals  28,- 
400  -T-  .42  =  67,620  Ib.  per  square  inch. 

Elastic  Limit. — The  elastic  limit  is  the  smallest  load,  reduced 
to  one  square  inch  of  area,  which  will  produce  a  permanent  set 
or  distortion  of  the  material.  Thus  in  a  tension  test  if  the  cross- 
section  is  .68  sq.  in.  and  a  permanent  elongation  or  set  is  just 
produced  by  a  load  of  27,600  Ib.,  the  elastic  limit  is  at  27,600  -i- 
.68  ==  40,600. 

Elongation. — A  certain  length  being  marked  off  on  the  test 
piece  as  described  in  [3],  [4],  the  percentage  of  elongation  is 


MATERIALS. 


27 


found  by  dividing  the  actual  extension  of  the  Jength  just  before 
rupture  by  the  original  length,  and  reducing  to  per  cent.  Thus 
if  a  length  of  8  in.  is  marked  off  on  the  test  piece  and  if  the 
length  between  the  same  marks  at  fracture  is  10.2  in.,  the  actual 
elongation  is  2.2  in.  and  the  percentage  elongation  is  220  -f-  8  = 
27.5  per  cent.  When  a  test  piece  is  first  put  under  load  the 

f "• 


i 


r\ 


Fig.  1.    Test   Piece   for   Iron   Plate. 


elongation  is  distributed  nearly  uniformly  over  its  length.  This 
continues  until  the  piece  begins  to  neck  down  near  the  point  of 
final  fracture.  Nearly  all  of  the  remaining  elongation  is  re- 
stricted to  the  immediate  vicinity  of  this  point.  Hence  the  per- 
centage elongation  with  short  length  of  test  piece  may  be  much 


CO 


1     H g- M      » 

U 16'Vo  20" *J 

Fig.  2.    Test   Piece  for   Steel. 

greater  than  with  a  long  piece.  A  few  years  ago,  for  example, 
when  test  pieces  2  in.  long  were  not  uncommon,  the  actual  elon- 
gation might  be  nearly  i  in.,  and  thus  percentage  elongations 
approaching  50  per  cent  were  found.  In  modern  practice  the 
length  of  a  test  piece  is  usually  8  in.  and  values  of  the  percent- 
age elongation  over  30  per  cent  even  with  vastly  superior  ma- 
terial, are  rarely  met  with.  In  reporting  elongation  the  length 
used  should  always  be  stated. 


,t 

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( 

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1 

•i 

1 

r*1 

i-  —  *j 

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Fig.  3.    Test  Piece  for  Steel. 

Reduction  of  Area. — The  percentage  reduction  of  area  is 
found  by  substracting  the  final  area  of  the  section  at  the  point  of 
fracture  from  the  original  area  at  the  same  point,  dividing  the 


PRACTICAL  MARINE  ENGINEERING. 


difference  by  the  latter,  and  reducing  to  per  cent.  Thus  if  the 
original  area  is  .68  sq.  in.  and  the  final  area  is  .36  sq.  in.,  the 
actual  reduction  is  .68  —  .36  =  .32  sq.  in.,  and  the  percentage 
reduction  is  3200  -=-  68  =  47.5  per  cent. 

[3]  Test  Pieces  for  Iron. 

In  modern  practice  the  form  of  test  pieces  for  iron  is  usually 


Fig.  4.     Plate    with    Coupon. 

the  same  as  for  steel,  and  as  described  in  [4] .  The  form  of  test 
piece  for  wrought  iron  plate  prescribed  by  the  U.  S.  Board  of 
Supervising  Inspectors  of  Steam  Vessels  is,  however,  somewhat 
different,  and  is  illustrated  in  Fig.  I.  If  the  plate  is  5-16  in. 
thick  or  less,  the  width  at  the  reduced  section  must  be  one  inch. 


U---8- 

Fig.  5.    Round  Test  Piece. 

If  the  plate  is  over  5-16  in.  in  thickness,  the  width  of  the  piece 
must  be  reduced  so  that  the  cross-sectional  area  at  the  reduced 
section  shall  be  about  .4  sq.  in.,  but  it  must  not  be  greater  than 
.45  sq.  in.  nor  less  than  .35  sq.  in. 

r 


Fig.  6.     Bending  Test.  Fig.  8.    Angle  Test. 

[4]  Test  Pieces  for  Steel  and  Other  Materials. 

Fig.  2  shows  the  form  of  test  piece  for  tension  prescribed 
by  the  Navy  Department  for  tests  of  steel  plate  for  naval  uses. 

Fig.  3  shows  the  form  prescribed  by  the  Association  of 
American  Steel  Manufacturers,  and  adopted  by  the  U.  S.  Board 
of  Supervising  Inspectors  of  Steam  Vessels.  The  test  piece  for 


MATERIALS. 


29 


plates  is  cut  from  a  "coupon,"  as  it  is  called,  left  on  one  corner 
of  the  plate  as  shown  at  A,  Fig.  4.  The  U.  S.  law  requires  fur- 
ther that: 

"Every,  iron  or  steel  plate  intended  for  the  construction  of 
boilers  to  be  used  on  steam  vessels  shall  be  stamped  by  the 
manufacturer  in  the  following  manner :  At  the  diagonal  corners, 
at  a  distance  of  about  4  in.  from  the  edges  and  at  or  near  the 
center  of  the  plate,  with  the  name  of  the  manufacturer,  the  place 
where  manufactured,  and  the  number  of  pounds  tensile  strain 
it  will  bear  to  the  sectional  square  inch." 

Fig.  5  shows  the  usual  round  form  of  test  piece  for  all  ma- 
terial except  plates. 

[5]  Bending,  Quenching  and  Hammer  Tests. 

The  nature  of  these  tests  has  already  been  described  in  Sec. 
S,  [51,  (n),  (12). 

Fig.  6  illustrates  a  cold  bending  test  on  a  piece  of  steel 
plate.  A  drift  test  is  also  sometimes  required.  This  is  illus- 
trated in  Fig.  7,  and  consists  in  driving  taper  drifts  of  con- 


Fig.  7.    Drift  Test. 

tinually  increasing  size  into  a  punched  or  drilled  hole  until  the 
diameter  is  increased  to  at  least  twice  its  original  size.  The 
metal  must  stand  this  test  without  sign  of  fracture  about  the 
edges  of  the  hole. 

Bending  tests  for  angle  and  Tee  irons,  as  referred  to  in  Sec. 
5,  [5],  (12),  are  also  illustrated  in  Fig.  8. 


PRACTICAL  MARINE  ENGINEERING. 


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FUELS.  31 


CHAPTER  II. 

FUELS. 

Sec.  ii.    COAI,. 
[i]  Composition  and  General  Properties. 

The  principal  fuel  for  engineering  purposes  is  coal.  It  con- 
sists of  the  following  chief  substances. 

(A)  Uncrystallized  Carbon. 

(B)  Volatile    Hydrocarbons.     Hydrocarbons     are     chemical 
substances  formed  of  carbon  and  hydrogen  in  certain  propor- 
tions.     They  often  become  partially  oxidized*  by  the  union  of 
part  of  their  hydrogen  with  oxygen,  in  the  same  proportion  as 
in  water.     Upon  the  application  of  heat  to  the  coal  they  escape 
in  the  form  of  gas,  and  are  hence  said  to  be  volatile. 

(C)  Nitrogen  and  Oxygen.     These  gases,  the  constituents  of 
air,  are  also  found,  the  latter  in  addition  to  this  amount  joined 
to  the  hydrogen  as  above  referred  to. 

(D)  Sulphur.     This  is  found  in  small  amounts,  chiefly  as  a 
part  of  the  mineral  known  as  iron  pyrites-^.    The  proportion  of 
sulphur  is  rarely  above  three  per  cent  and  usually,  much  less. 

(E)  Ash.     This  consists  of  the  earthy  and  incombustible 
substances  present  as  impurities  in  the  coal. 

Coal  may  be  roughly  divided  into  two  chief  varieties,  An- 
thracite and  Bituminous,  with  intermediate  grades,  Semi-anthra- 
cite and  Semi-bituminous  occupying  the  general  middle  ground 
between  the  two.  In  the  present  chapter  we  shall  frequently 
use  the  terms  anthracite  and  bituminous  as  denoting  the  general 
division  into  the  two  chief  varieties,  as  above  noted. 

Anthracite  coal  is  sold  commercially  in  hard,  compact 
lumps,  showing  a  shiny,  smooth  surface  when  first  broken. 


*  Oxidized  means  united  with  oxygen. 

t  Iron  pyrites  is  a  mineral  formed  of  iron  and  sulphur  in  the  proportion 
of  46.7  parts  of  iron  to  53.3  of  sulphur. 


32  PRACTICAL  MARINE  ENGINEERING. 

Bituminous  coal  is  relatively  soft  and  is  sold  commercially  in 
lumps  or  irregular  size.  It  crumbles  easily,  showing  often  a 
rather  dull  surface  when  broken. 

In  the  anthracite  coal  the  proportion  of  volatile  matter 
varies  from  3  to  10  per  cent;  in  semi-anthracite  and  semi-bit- 
uminous, from  10  to  20  per  cent,  and  in  bituminous,  from  20  to 
50  per  cent.  The  amount  of  ash  in  good  coal  should  not  ex- 
ceed from  8  to  10  pen  cent,  while  occasionally  it  falls  as  low  as 
5  per  cent.  Anthracite  coal  is  graded  commercially,  according 
to  size,  the  chief  terms  being  the  following,  in  the  order  of  in- 
creasing size :  Buckwheat,  pea,  chestnut,  stone,  egg,  broken  and 
lump. 

[a].    Combustion. 

Combustion  means  simply  the  chemical  union  of  a  substance 
with  oxygen.  The  oxygen  is  furnished  by  the  air,  which  con- 
tains oxygen  and  nitrogen.  These  in  air  are  not  in  chemical 
union,  but  simply  as  a  mixture,  in  the  proportion  by  weight  of 
twenty-three  parts  oxygen  to  seventy-seven  parts  nitrogen  in 
one  hundred  parts  of  air.  When  bodies  enter  into  combustion, 
or  into  combustion  with  oxygen,  heat  is  set  free,  and  the  prod- 
ucts formed  by  the  combustion  are  very  much  hotter  than  the 
original  fuel  and  oxygen. 

The  manner  in  which  coal  burns,  or  enters  into  combustion, 
depends  upon  its  composition  and  upon  the  nature  of  the  fire 
and  the  supply  of  air.  The  elements  available  for  the  libera- 
tion of  heat  are  the  carbon  and  the  hydrogen.  Small  quantities 
of  sulphur  are  frequently  present,  but  the  amount  is  so  small 
and  the  heating  power  so  feeble  that  its  influence  may  be  neg- 
lected. A  pound  of  pure  carbon  requires  for  its  complete  com- 
bustion, 2  2-3  pounds  of  oxygen,  and  the  result  is  3  2-3  pounds 
of  carbonic  acid  or  carbon  dioxide  in  the  form  of  gas.  The  total 
amount  of  heat  set  free  in  this  operation  is  about  14,500  heat 
units.  Now,  since  the  proportion  of  oxygen  in  the  air  is  about 
23  per  cent,  the  number  of  pounds  of  air  required  per  pound  of 
carbon  will  be  2  2-3  -r-  .23,  or  2.66  -=-  .23,  or  about  12.  Similarly 
a  pound  of  pure  hydrogen  requires  for  its  complete  combustion, 
8  pounds  of  oxygen,  and  the  result  is  9  pounds  of  water  vapor. 
The  total  amount  of  heat  set  free  in  this  operation  is  about  62,- 
ooo  heat  units.  In  the  same  way  as  above,  it  follows  that  the 
combustion  of  a  pound  of  hydrogen  will  require  the  presence 
of  8  -f-  .23,  or  about  35  pounds  of  air.  The  amount  of  hydro- 


FUELS.  33 

gen,  however,  is  usually  small,  and  allowing  for  the  ash  the 
amount  of  air  necessary  to  barely  furnish  the  oxygen  required 
for  one  pound  of  fuel  is  about  12,  or  substantially  the  same  as 
for  one  pound  of  carbon.  In  practice,  however,  it  is  found  that 
this  would  be  insufficient  to  maintain  the  draft,  nor  could  we 
expect  that  the  air  would  be  so  distributed  as  to  give  exactly 
the  right  amount  of  oxygen  at  the  right  place.  It  is,  therefore, 
necessary  practically,  to  provide  a  large  excess  of  air  and  the 
amount  actually  passing  into  the  furnaces  is  usually  not  less 
than  18  or  20  pounds  per  pound  of  coal,  and  may  even  consider- 
ably exceed  this  amount.  At  12.5  cu.  ft.  per  pound  this  will  give 
for  the  volume  of  air  required  per  pound  of  coal  from  225  to  250 
cu.  ft.  and  upward. 

Let  us  now  consider  the  process  of  combustion  with  bitum- 
inous or  semi-bituminous  coal.  When  such  coal  is  put  on  the 
fire  the  first  result  is  not  a  combustion  of  the  carbon,  but  a  dis- 
tillation or  driving  off  of  the  hydrocarbons  in  the  form  of  gas, 
and  until  this  operation  is  nearly  completed  there  will  be  little 
or  no  combustion  of  the  carbon.  During  this  first  operation  of 
distillation,  heat  is  absorbed  by  the  fresh  coal  from  the  re- 
mainder of  the  fire  for  the  liberation  of  these  gases  which  are 
substantially  the  same  as  those  forming  ordinary  illuminat- 
ing gas.  After  these  gases  are  liberated  from  the  coal  they 
rise  into  the  furnace  and  combustion  chamber.  Here,  if 
they  meet  with  a  suitable  supply  of  air  at  a  proper  tempera- 
ture, they  will  be  burned,  both  carbon  and  hydrogen,  and 
will  thus  set  free  all  the  heat  which  is  obtainable  from  them.  If 
the  air  is  insufficient  in  amount  the  gases  will  be  only  partly  con- 
sumed, the  oxygen  uniting  most  readily  with  the  hydrogen  and 
leaving  the  carbon  in  fine  particles  to  form  smoke  or  soot,  accord- 
ing as  they  float  away  with  the  products  of  combustion,  or  be- 
come closely  packed  together  on  some  of  the  surfaces  of  the 
boiler.  If  the  air  is  not  sufficiently  hot  likewise,  we  may  have 
a  partial  combustion  resulting  in  burning  the  hydrogen  into 
water  vapor  and  in  setting  the  carbon  free  as  smoke  or  soot  as 
before.  If,  however,  the  temperature  is  too  low  the  gases  may 
become  chilled  and  pass  off  as  a  wrhole  unburnt,  thus  carrying 
away  not  only  their  own  heat  of  combustion,  but  also  the  heat 
\vhich  was  absorbed  for  their  liberation.  If,  on  the  other  hand, 
hydrocarbon  gases  are  subjected  to  a  very  high  temperature  be- 
fore being  mixed  with  the  air,  they  will  become  more  or  less 


34  PRACTICAL  MARINE  ENGINEERING. 

broken  up  into  free  hydrogen  and  carbon  in  fine  particles.  If 
these  are  kept  at  a  temperature  high  enough  for  ignition  and 
are  supplied  with  oxygen,  they  will  burn ;  but  if  they  fall  below 
the  proper  temperature  they  pass  off  unburnt,  the  carbon  con- 
stituting smoke  or  soot,  as  before.  Smoke  is,  therefore,  the 
sign  of  a  fuel  containing  hydrocarbons,  and  of  a  more  or  less 
imperfect  combustion.  The  actual  amount  of  fuel  lost  in  or- 
dinary smoke  is,  however,  quite  small ;  so  small  that  it  is  often 
considered  as  having  no  significant  influence  on  the  question 
of  economy.  Hence,  smoke  prevention  is  often  considered  as 
hardly  worth  special  effort,  so  far  as  the  saving  of  fuel  alone  is 
concerned.  There  may  be  other  losses,  however,  in  connection 
with  the  general  condition  of  which  smoke  is  an  indication,  and 
any  mode  of  design  and  of  general  operation  which  reduces  the 
smoke  formation  will  usually  tend  toward  economy  of  combus- 
tion. 

We  have  already  seen  that  the  conditions  for  burning  the 
hydrocarbon  gas  are  high  temperature  and  an  air  supply  above 
the  grates  and  in  the  combustion  chamber.  We  have  here, 
then,  one  of  the  reasons  for  providing  openings  for  the  proper 
admission  of  air  above  the  grates  as  well  as  underneath. 

Let  us  now  return  to  the  residue  left  on  the  grates  after  the 
escape  of  the  hydrocarbon  gases.  During  this  part  of  the 
operation  certain  kinds  of  bituminous  coal  swell  up  and  cake 
more  or  less  firmly  together  on  the  grate.  Such  are  called 
caking  coals.  The  swelling  up  is  due  to  the  formation  of  gas 
in  the  midst  of  the  coal  and  to  its  efforts  to  escape,  while  the 
caking  is  due  to  a  partial'  softening  or  melting  of  the  substance 
under  heat  as  the  hydrocarbons  are  set  free.  Other  kinds  of 
bituminous  coal  undergo  little  change  in  their  external  form, 
while  still  others  break  up  into  small  particles  or  grains.  Those 
latter  varieties  are  called  non-caking  or  free-burning  coals.  In 
any  case  the  residue,  after  the  hydrocarbons  are  set  free,  is 
called  coke  and  consists  of  nearly  pure  carbon  with' ash. 

As  we  have  already  seen  the  carbon  burns  by  uniting  with 
oxygen,  and  this  must  take  place  at  the  burning  lump  itself. 
Hence,  it  is  necessary  that  the  air  should  penetrate  thoroughly 
all  parts  of  the  fire,  and  to  this  end  it  is  brought  in,  in  part  at 
least,  under  the  grate  and  by  the  draft  pressure  is  forced  up- 
ward through  the  mass  of  burning  coal.  If  the  fire  is  rather 
thick  the  operation  proceeds  in  the  following  way.  The  car- 


FUELS.  35 

bon  and  oxygen  first  unite  in  complete  combustion,  I  pound  of 
carbon  tq  2  2-3  pounds  of  oxygen,  and  the  product,  carbon  di- 
oxide, proceeds  upward  through  the  fire.  As  this  gas  comes 
in  contact,  however,  with  the  cooler  coal  in  the  midst  or  near 
the  top  of  the  bed  of  fuel  it  absorbs  some  of  the  carbon  and  be- 
comes changed  to  a  combination  in  the  proportion  of  i  pound 
of  carbon  to  I  1-3  pounds  of  oxygen.  This  gas  is  called  carbon 
monoxide.  In  this  operation  also  is  absorbed  back  again  more 
than  two-thirds  of  the  heat  which  the  first  combustion  had  liber- 
ated. If  the  gas  should  escape  unburnt,  a  serious  loss  would 
result,  as  only  about  4,450  heat  units  or  less  than  one-third  of 
the  heat  available  in  the  carbon  would  have  been  liberated.  If, 
however,  the  gas  finds  air  above  the  grate  and  a  suitable  tem- 
perature, the  carbon  which  was  absorbed  is  burnt  out  again  and 
the  corresponding  heat  is  given  back,  so  that  the  final  result 
is  the  complete  combustion  of  the  carbon  and  the  liberation  of 
all  the  heat  possible.  The  formation  of  carbon  monoxide  in 
this  way  shows  again  the  need  of  admitting  air  above  the  grate, 
as  well  as  underneath.  This  gas  burns  with  the  peculiar  blue 
flame  so  often  seen,  especially  after  a  fresh  firing  with  anthracite 
coal,  and  the  presence  of  this  flame  thus  indicates  the  formation 
and  recombustion  of  carbon  monoxide  in  the  way  described. 
After  the  coal  has  all  been  thoroughly  ignited  and  raised  to  a 
bright  glowing  heat,  the  combustion  into  carbon  dioxide  is  com- 
pleted at  once,  and  there  is  little  or  no  formation  of  carbon 
monoxide  to  be  burned  as  a  gas  above  the  grate.  The  thinner 
the  fire  the  more  quickly  is  this  condition  reached. 

The  combustion  of  semi-anthracite  and  of  anthracite  coal 
proceeds  in  the  same  general  manner  as  for  bituminous  coal, 
except  that  the  period  of  distillation  becomes  shorter  and  less 
important  as  the  proportion  of  hydrocarbon  is  decreased.  It 
thus  results  that  an  ordinary  anthracite  coal  burns  almost  en- 
tirely in  the  manner  described  for  the  coke  residue  of  bitumin- 
ous coal,  except  that  in  consequence  of  the  lower  temperature 
of  the  fuel  during  the  early  stages  of  combustion,  there  is  apt  to 
be  a  more  pronounced  formation  of  carbon  monoxide  for  the 
combustion  of  which  there  must  be  a  supply  of  air  above  the 
grate  as  already  noted. 

[3].  Impurities  in  Coal.    Clinker  Formation. 

The  chief  impurities  in  coal  may  be  divided  as  follows  :  (A) 
Nearly  infusible  slate,  stone,  and  earthy  matter  either  in  separate 


36  PRACTICAL  MARINE  ENGINEERING. 

lumps  or  distributed  through  the  coal  as  a  whole,  thus  giving  it  a 
low  carbon  value.  (B)  Mineral  materials  more  or  less  fusible,  and 
thus  capable  of  melting  and  forming  a  slag  which  uniting  with 
the  ash  and  slate  forms  clinker.  Substances  liable  to  be  pres- 
ent in  coal  and  which  are  more  or  less  fusible  at  the  high  tem- 
peratures in  the  furnaces  are  :  Potash,  soda,  lime  and  silica.  The 
melting  point  of  these  substances  is  also  considerably  lowered 
by  mixing  with  iron  oxide,  which  is  always  formed  by  the  oxida- 
tion or  combustion  of  iron  pyrites.  The  presence  of  this  sub- 
stance in  the  coal  will  thus  result  in  lowering  the  melting  point 
of  the  other  mineral  earths  and  impurities,  and  in  the  greater  li- 
ability to  form  clinker.  This  formation  of  clinker  may  be  so 
considerable  as  to  seriously  interfere  with  the  combustion  of  the 
coal,  and  in  such  cases  its  removal  must  be  carefully  attended  to 
from  time  to  time  in  order  to  keep  the  fires  in  good  condition. 
Iron  oxide,  or  common  iron  rust  as  we  call  it  more  famil- 
iarly, will  give  to  the  ashes  a  reddish  tinge  so  that  such  a  color 
noted  in  the  ash  may  usually  be  accepted  as  an  indication  of  the 
presence  of  iron  pyrites  in  the  coal,  with  the  various  results 
which  have  been  already  noted.  Its  presence  in  any  consider- 
able amount  is  also  usually  shown  by  a  yellowish  or  brassy  ap- 
pearance of  the  coal.  For  the  formation  of  little  or  no  clinker 
a  coal  should  have  little  or  no  alkali,  lime,  or  pyrites.  Such  coal 
in  burning  gives  a  nearly  white,  soft  and  friable  ash. 

[4].  Weathering  of  Coal. 

When  coal  is  exposed  to  the  air  and  weather  for  a  con- 
siderable period  of  time  there  is  a  slow  absorption  of  oxygen, 
and  thus  a  real  combustion  and  wasting  of  the  fuel  value 
of  the  coal.  It  thus  results  that  the  coal  during  this 
operation  is  really  burning  up,  though  at  a  rate  so  slow 
that  the  heat  developed  is  hardly  appreciable  and  the  change  in 
the  outward  appearance  of  the  coal  is  so  gradual  as  to  escape 
ordinary  notice.  The  hydrocarbons  are  much  more  readily  sub- 
ject to  this  operation  of  gradual  oxidation  or  combustion  than 
pure  carbon,  the  latter  entering  only  with  great  difficulty  into 
union  with  oxygen  at  ordinary  temperatures.  It  thus  follows 
that  bituminous  coals  are  much  more  subject  to  waste  and 
change  by  weathering  than  anthracite  coals.  In  addition  to  the 
loss  due  to  this  slow  combustion  there  is  often  a  gradual  escape 
of  gaseous  hydrocarbons  imprisoned  within  the  lumps,  or  a 


FUELS.  37 

gradual  vaporization  of  liquid  hydrocarbons  and  their  es- 
cape as  vapor.  Such  losses  also  are,  of  course,  more  marked 
with  bituminous  than  with  anthracite  coals.  A  bitum- 
inous caking  coal  often  becomes  changed  to  a  non-caking  coal 
after  exposure  to  the  air  and  weather  for  a  considerable  period 
of  time. 

The  chief  external  conditions  which  may  influence  weather- 
ing are  moisture  and  heat.  If  the  coal  contains  no  iron  pyrites, 
moisture  is  believed  to  slightly  retard  the  operation  of  slow  com- 
bustion, and  thus  to  act  beneficially  rather  than  the  reverse.  If 
iron  pyrites  is  present  in  the  coal,  the  conditions  are  changed. 
Iron  pyrites  oxidize  with  comparative  readiness  at  ordinary  tem- 
peratures, both  the  sulphur  and  iron  uniting  with  the  oxygen.  It 
thus  tends  to  set  up  the  operation  of  oxidation  and  to  break  up 
the  lump  into  small  bits,  while  the  heat  developed  is  a  further 
aid  to  the  continuance  of  the  process.  The  oxidation  of  iron 
pyrites  is,  moreover,  much  aided  by  moisture,  which,  therefore, 
with  such  coals,  becomes  a  distinct  disadvantage.  In  any  event 
a  coal  with  iron  pyrites  may  be  expected  to  suffer  more  seriously 
fay  weathering  than  one  free  from  this  substance.  In  extreme 
cases  the  oxidation  of  the  pyrites  has  caused  the  crumbling  of 
the  coal  into  such  small  bits  that  it  has  become  nearly  worthless 
for  its  original  purposes. 

Heat  in  general  always  increases  the  activity  of  this  slow 
combustion,  and  hence  tends'  to  increase  the  loss  due  to  weath- 
ering. The  heat  developed  by  slow  oxidation  in  the  interior  of 
large  piles  or  masses  of  coal  escapes  with  great  difficulty  and 
thus  accumulates  and  raises  the  temperature,  thus  making  the 
conditions  still  more  favorable  for  the  continuance  of  the 
process.  So  far  as  this  effect  goes,  therefore,  the  loss  would 
be  more  serious  in  large  piles  than  in  small.  This  is,  however, 
offset  by  the  greater  difficulty  which  the  oxygen  has  in  penetrat- 
ing to  the  interior  of  the  pile  as  it  is  larger  in  size.  It  results 
that  with  other  things  equal  there  is  no  great  difference  in  the 
loss  due  to  weathering  with  coal  either  in  large  or  in  small  bulk. 

[5].  Spontaneous  Combustion. 

We  have  already  seen  under  the  head  of  weathering  that 
coal  at  ordinary  temperatures  is  subject  to  a  very  slow 
oxidation,  or  combustion,  which  gradually  wastes  away  its 
fuel  value.  When  the  coal  is  freshly  mined  this  oxi- 


38  PRACTICAL  MARINE  ENGINEERING. 

dation  seems  to  be  especially  active  due  to  the  property 
which  carbon  has  of  absorbing  or  condensing  gases  upon 
its  surface.  The  volume  of  oxygen  that  different  coals  are 
capable  of  absorbing  varies  from  \l/\  to  3  times  the  volume  of 
the  coal.  The  oxygen  thus  absorbed  is  very'  active  chemically, 
due  to  the  fact  that  coming  from  the  air  it  is  absorbed  more 
readily  than  the  nitrogen,  and  is  thus  less  diluted  than  in  the  air. 
This  absorption  is  itself  attended  by  the  production  of  heat,  and 
this  heat,  in  conjunction  with  other  conditions  favorable  to 
chemical  action,  brings  about  an  oxidation  of  the  hydrocarbons 
of  the  coal,  thus  generating  still  more  heat. 

Xow,  if  the  coal  is  in  small  bulk  and  well  ventilated,  there 
will  be  little  chance  for  the  gradual  accumulation  of  the  heat  and 
a  consequent  rise  of  temperature.  A  few  lumps  of  coal  exposed 
to  the  open  air  may  lose  much  by  weathering  in  the  course  of 
six  months  or  a  year,  but  the  heat  set  free  will  readily  escape 
and  the  rise  of  temperature  will  be  unnoticeable.  If,  on  the 
contrary,  the  coal  is  in  large  bulk,  or  is  confined  in  bunkers  with 
little  or  no  ventilation,  the  heat  developed  by  slow  oxidation 
will  be  imprisoned  and  the  temperature  may  gradually  rise  to 
the  point  wrhere  active  combustion  will  proceed  according  to  the 
supply  of  air  available. 

It  thus  appears  that  there  may  be  danger  from  no  ventila- 
tion or  from  insufficient  ventilation.  Opinions  differ  on  these 
points,  but  it  may  probably  be  accepted  that  unless  the  ventila- 
tion can  be  made  thorough,  the  compartment  should  be  kept 
tight  and  the  air  excluded  as  much  as  possible.  At  the  same 
time  before  such  closed  compartments  or  bunkers  are  entered 
with  a  light  they  should  be  thoroughly  ventilated,  especially  if 
the  coal  is  of  a  quality  likely  to  freely  disengage  hydrocarbon 
gases. 

A  further  important  point  to  be  noted  relates  to  the  in- 
fluence which  the  initial  temperature  has  on  the  rapidity  of 
chemical  actions  of  this  kind.  Below  a  temperature  of  100 
F.  the  action  will  go  on  slowly  with  little  chance  of  undue  heat- 
ing taking  place,  but  as  soon  as  the  temperature  rises  much 
above  100  F.,  especially  with  certain  coals,  spontaneous  ignition 
is  only  a  question  of  time. 

It  appears,  therefore,  that  the  true  index  of  the  danger  of 
spontaneous  combustion  must  be  taken  as  the  capacity  of  the 
coal  for  absorbing  or  condensing  gases  in  its  outer  layers  or 


FUELS.  39 

near  its  surface.  This  in  turn  will  be  shown  by  the  amount  of 
moisture  which  it  can  absorb  from  the  air.  A  coal  which  ab- 
sorbs a  large  amount  of  moisture  from  the  air  will  at  the  same 
time  absorb  a  large  amount  of  oxygen,  and  will,  therefore,  be 
relatively  a  dangerous  coal  as  regards  spontaneous  combustion, 
while  on  the  other  hand  a  coal  which  absorbs  but  a  small  amount 
of  moisture  from  the  air  will  likewise  absorb  but  little  oxygen, 
and  will  be  comparatively  safe  as  regards  spontaneous  combus- 
tion. The  percentage  of  moisture  which  can  be  absorbed  from 
the  air  by  coal  is  found  to  vary  from  about  2.5  to  10  per  cent, 
and  experience  has  shown  that  the  liability  to  spontaneous  com- 
bustion varies  closely  with  this  percentage. 

In  general  then  the  liability  to  spontaneous  combustion  de- 
pends on, 

(1)  The  size  of  the  cargo  or  compartment,  increasing  as 
the  bulk  increases. 

(2)  The    size   of   the   coal,   increasing   as   the   lumps   are 
smaller,  and  thus  present  relatively  more  surface. 

(3)  The  presence  of  iron  pyrites  with  moisture.      Iron  py- 
rites has  sometimes  been  thought  a  possible  direct  cause   of 
spontaneous  combustion,  but  the  proportion  of  this  substance 
is  small,  rarely  rising  above  3  or  4  per  cent,  and  the  heat  de- 
veloped by  the  combustion  of  sulphur  and  iron  is  very  much  less 
per  pound  than  for  carbon  and  hydrogen.     The  heat  developed 
by  the  oxidation  of  iron  pyrites  is,  therefore,  hardly  sufficient 
to  do  more  than  help  along  the  general  condition  of  slow  com- 
bustion as  referred  to  above.      In  another  way,  however,  the 
presence  of  the  pyrites  may  have  an  important  influence  on  the 
result.      The  presence  of  moisture  favors  the  oxidation  of  the 
pyrites  and  as  a  result  of  this  it  will  swell  and  tend  to  split  up 
the  coal,  thus  decreasing  the  size  of  the  lump  and  increasing  its 
absorbing  surface.      It  is  presumably  in  this  way  that  the  pres- 
ence of  iron  pyrites  tends  to  aid  spontaneous  combustion. 

(4)  The  quality  of  the  coal.     Bituminous  and  semi-bitum- 
inous coals  are  more  liable  to  spontaneous  combustion  than  an- 
thracite coal,  because  they  are  more  porous  and  friable   and 
present  more  absorbing  surface,  and,  furthermore,  are  rich,  in 
easily  oxidisable  hydrocarbons  as  already  noted  in  [i].     In  fact, 
under  usual  conditions  anthracite  coal  may  be  considered  as 
beyond  danger  of  this  character. 

(5)  The  amount  of  weathering  the  coal  has  had.     If  it  has 


40  PRACTICAL  MARINE  ENGINEERING, 

been  exposed  to  considerable  weathering  and  has  since  been 
subjected  to  but  little  breakage,  then  additional  oxygen  will  be 
absorbed,  but  very  slowly,  and  the  danger  of  spontaneous  com- 
bustion will  be  very  small  indeed. 

(6)  The  temperature  of  the  bunkers  or  compartments  as 
affected  by  the  nearness  to  boilers,  funnel,  etc. 

(7)  Ventilation  of  cargo.     For  ventilation  to  be  thorough- 
ly effective  cold  air  would  have  to  sweep  continuously  and  freely 
through  every  part,  a  condition  hardly  possible  to  attain  with  a 
coal  cargo.     Anything  short  of  this  may  possibly  increase  the 
danger  by  supplying  just  about  the  right  amount  of  air  to  create 
the  maximum  heating. 

The  gases  imprisoned  within  the  coal,  reference  to  which 
was  made  in  [4] ,  may  also  escape  and  collect  in  a  closed  and  un- 
ventilated  compartment  or  bunker,  and  upon  the  later  introduc- 
tion of  a  light  an  explosion  may  result.  This  is  exactly  similar 
to  the  way  in  which  firedamp  explosions  in  mines  may  occur. 

[6].    Corrosion. 

As  a  further  possible  result  of  the  presence  of  iron  py- 
rites and  the  sulphur  which  is  one  of  its  constituents, 
the  corrosion  of  the  metal  surfaces  of  the  boiler  may  be 
mentioned.  Sulphur  in  burning  in  the  presence  of  moisture 
may  produce  sulphuric  acid,  and  this  may  seriously  corrode  such 
surfaces  as  it  comes  in  contact  with,  especially  if  there  is  oppor- 
tunity for  its  gradual  action  during  periods  when  the  boiler  is 
not  in  active  use.  The  conditions  necessary  for  the  formation 
of  sulphuric  acid  are,  however,  not  commonly  present  in  marine 
boilers,  and  the  danger  of  corrosion  from  the  combustion  of  iron 
pyrites  is  not  usually  considered  as  serious. 

[7],  Transportation  and  Stowage.    , 

In  general  anthracite  coal  bears  transportation  and  handling 
better  than  bituminous  on  account  of  its  greater  hardness.  It 
also  stows  more  evenly  on  account  of  the  greater  uniformity  in 
size  of  lump. 

The  weight  of  coal  in  the  solid  lump  is  from  70  to  80  Ib. 
per  cubic  foot  for  bituminous  grades,  and  from  851  or  90  to  100 
Ib.  per  cubic  foot  for  anthracite  grades.  When  broken  up  in  or- 
dinary commercial  sizes,  however,  its  weight  in  bulk  is  usually 
from  50  to  54  Ib.  per  cubic  foot  for  bituminous,  and  from  53  to 
58  Ib.  per  cubic  foot  for  anthracite.  These  weights  correspond 


FUELS.  41 

to  an  allowance  of  from  42  to  45  cu.  ft.  per  ton  of  2,240  Ib.  for 
bituminous  grades  and  from  39  to  42  cu.  ft.  per  ton  for  anthra- 
cite grades. 

[8].  General  Comparison  Between  Bituminous  and  Anthracite 

Coal. 

As  between  the  two  kinds  of  coal,  bituminous  burns 
more  readily  than  anthracite,  and  requires  a  somewhat 
lower  temperature  for  the  process.  This  is  because  with 
the  former  the  hydrocarbon  gases  are  first  driven  off  and  burnt, 
while  the  coke  residue  is  left  in  a  light  and  porous  condition, 
and  thus  well  suited  for  intimate  contact  with  the  oxygen,  and 
for  rapid  elevation  to  the  temperature  of  ignition.  On  the  other 
hand,  with  anthracite  coal  the  hydrocarbon  gases  are  so  small 
in  amount  as  to  have  little  influence  on  the  process,  and  the  coal 
has,  therefore,  to  burn  as  compact,  solid  lumps  of  carbon,  with 
little  opportunity  for  contact  with  the  oxygen  except  at  the 
outer  surface. 

It  results  that  under  the  same  conditions  of  draft,  firing, 
etc.,  considerably  more  coal  can  be  burned  per  square  foot  of 
grate  surface  with  bituminous  than  with  anthracite.  The  excess 
of  the  former  will  depend,  of  course,  on  the  special  conditions, 
but  will  usually  reach  from  20  per  cent  to  40  per  cent,  or  even 
more. 

From  the  explanation  given  in  [2]  it  will  be  clearly  seen 
that  smoke  and  soot  are  chiefly  the  products  of  bituminous  coal. 
With  anthracite  coal,  immediately  after  firing,  a  slight  show  of 
smoke  may  be  formed,  but  with  neither  the  volume  nor  density 
of  the  smoke  formed  by  bituminous  coal,  while  the  soot  formed 
with  anthracite  is  too  small  in  quantity  to  be  of  any  significance. 

Bituminous  coal,  as  we  have  seen,  is  more  liable  to  spon- 
taneous combustion  than  anthracite,  and  the  loss  by  weathering 
is  usually  more  serious. 

A  good  quality  of  free-burning  semi-bituminous  coal  is 
usually  considered  as  the  best  variety  for  all  around  steaming 
purposes. 


Sec.  is.    BRIQUETTES  AND  ARTIFICIAL 

This  fuel  is  made  from  small  bits  of  coal,  coal  dust,  or  from 
certain  grades  of  coal  which  are  so  soft  or  crumbling  that  they 
cannot  be  readily  used  in  their  natural  state.  The  material  after 
selection  and  removal  of  impurities,  so  far  as  practicable,  is 


42  PRACTICAL  MARINE  ENGINEERING. 

reduced  to  powder  by  grinding,  and  is  then  mixed  with  some 
binding  material  and  pressed  into  cubes  or  blocks  weighing 
from  one  to  three  or  four  pounds  each.  The  binding  material 
is  usually  coal-tar,  asphalt,  crude  oil  refuse,  or  some  similar 
substance.  In  some  cases  a  caking  coal  has  been  used  by  heat- 
ing until  softening  occurs  and  then  pressing  into  moulds  while 
hot. 

The  character  of  such  fuels  will,  of  course,  depend  on  the 
nature  of  the  materials  of  which  they  are  made.  By  a  proper 
choice  of  the  ingredients  or  by  a  suitable  enriching  with  hydro- 
carbons in  the  form  of  pitch  or  crude  oil,  a  fuel  of  most  ex- 
cellent quality  may  be  made.  The  pressure  to  which  the  blocks 
are  subjected  is  so  great  that  the  materials  become  closely  com- 
pacted together  and  hold  their  form  with  no  more  breakage 
through  handling  than  with  a  good  quality  of  semi-bituminous 
or  even  semi-anthracite  coal.  The  best  grades  of  artificial  fuel 
ring  when  struck  and  absorb  little  or  no  water,  thus  showing  a 
compact  and  firm  structure  throughout.  They  ignite  readily 
and  burn  freely  without  an  excessive  formation  of  smoke,  hold- 
ing their  shape  without  crumbling  too  rapidly  on  the  grate. 
In  evaporative  power  the  best  briquettes  are  the  equivalent  of 
good  coal,  from  which  indeed  they  differ  chemically  in  no  es- 
sential character. 

The  weight  per  cubic  foot  and  the  number  of  cubic  feet  per 
ton  when  stowed  loosely  are  about  the  same  as  for  good  semi- 
bituminous  coal  of  like  quality.  If  packed  regularly  the  waste 
space  is  much  decreased  and  the  cubic  feet  per  ton  will  be  re- 
duced to  from  25  to  35. 


Sec.  13.    UQUID 

[i].  Composition. 

The  only  liquid  fuel  of  importance  to  the  engineer 
is  either  crude  petroleum  oil,  or  the  residue  left  after 
removing  from  the  crude  oil  by  distillation  the  lighter  con- 
stituents, consisting  of  naphtha,  illuminating  oil,  etc.  Crude 
petroleum  oil  is  a  liquid  of  brownish  tint  varying  from  light 
straw  to  almost  black.  It  consists  of  a  very  complex  mixture 
of  many  hydrocarbons.  Some  of  these  vaporize  very  easily  and 
escape  rapidly,  even  at  ordinary  temperatures.  Such  constitute 
the  naphthas  and  gasoline.  Next  in  order  come  the  con- 
stituents which  form  common  illuminating  oil  or  kerosene. 


FUELJ.  43 

Then  still  heavier  and  denser  come  the  lubricating  oils  of  vari- 
ous kinds.  After  the  removal  of  these  there  still  remains  a 
residue  capable  of  yielding  paraffine  and  vaseline,  and  last  of  all 
a  certain  amount  of  gas  tar  and  coke. 

When  the  process  of  refining  or  distillation  is  arrested  after 
the  removal  of  the  naphthas  and  illuminating  oils,  and  perhaps 
some  of  the  lubricating  oil,  the  residue  consists  of  a  rather  thick 
viscid  liquid,  not  readily  ignited  as  compared  with  the  crude  oil, 
but  under  proper  conditions  burning  readily  and  with  great  heat- 
ing power.  Such  residue  in  the  Russian  oil  wells  on  the  Cas- 
pian is  called  astatki.  It  constitutes  more  than  one-half  of  the 
crude  oil.  On  the  other  hand,  with  American  oils  the  similar 
residue  is  much  less  in  amount,  rarely  rising  to  one-third  of  the 
crude  oil.  Furthermore,  the  processes  of  refining  are  so  much 
superior  in  the  United  States  that  of  final  residue  after  the  re- 
moval of  all  marketable  products,  there  is  almost  nothing  left. 
With  the  best  modern  methods  of  treatment,  therefore,  the  use 
of  the  residue  after  partial  refinement  does  not  mean  the  utiliza- 
tion of  a  waste  or  by-product,  but  the  use  of  a  substance  having 
a  definite  market  value  for  other  and  long  established  uses. 
For  the  direct  use  of  crude  oil  the  same  is  true  in  still  higher 
degree,  so  that  under  modern  conditions  the  use  of  liquid  fuel 
means  simply  a  competition  with  the  various  other  industries 
involving  the  use  of  the  various  products  of  crude  petroleum  oil. 

[a].  Combustion. 

For  the  combustion  of  crude  oil  or  liquid  refuse,  two 
methods  are  in  use.  In  the  earlier  and  better  known  the  chief 
essential  is  fhat  the  liquid  must  be  "pulverized"  or  "at- 
omized"— that  is,  broken  up  into  a  very  fine  spray  and 
thus  brought  into  intimate  contact  with  the  oxygen  of  the  air. 
This  is  accomplished  by  special  devices  fitted  to  the  furnace  and 
called  "pulverizers''  or  "atomizers."  They  are  of  two  chief 
varieties  according  to  the  means  used — either  compressed  air  or 
steam.  In  each  the  oil  is  fed  by  pump  or  allowed  to  flow  by 
gravity  to  the  nozzle  of  the  device.  Here  it  is  caught  by  a  jet 
of  air  or  steam,  as  the  case  may  be,  issuing  near  or  through  it, 
and  by  this  means  is  thoroughly  broken  into  a  fine  spray  and 
blown  into  the  furnace  in  tliis  condition.  Once  the  fire  started, 
the  spray  is  ignited  as  it  issues  from  the  nozzle  so  that  the  re- 
sult is  a  long,  fiercely  burning  jet  of  flame  directed  into  the  fur- 

t 


44  PRACTICAL  MARINE  ENGINEERING. 

nace.  In  order  to  produce  the  conditions  best  for  complete 
combustion,  it  is  usually  found  advantageous  to  have  fire  brick 
so  disposed  as  to  take  the  direct  action  of  the  flame.  These 
bricks  become  heated  to  a  high  temperature  and  by  their  radiat- 
ing action  help  to  produce  and  maintain  a  temperature  suitable 
for  the  complete  combustion  of  all  gaseous  products  formed 
from  the  liquid  spray.  In  a  later  and  on  the  whole  more  effi- 
cient method  the  oil  is  first  vaporized  and  then  introduced  into 
the  furnace  as  a  vapor  and  there  burned  as  such. 

Under  proper  conditions,  and  especially  by  the  latter 
method,  oil  may  thus  be  burned  with  little  or  no  formation  of 
smoke  or  soot.  The  absence  of  all  soot  is  especially  favorable 
to  the  maintenance  of  a  high  efficiency  of  operation.  There  is 
furthermore  no  clinker  or  ash,  no  cleaning  of  fires,  no  opening 
of  furnace  doors  either  for  firing  or  cleaning,  and  no  handling 
of  ashes. 

[3],  Danger  of  Explosion. 

The  danger  of  explosion  or  of  the  formation  of  an 
explosive  mixture  by  the  slow  distillation  of  the  lighter 
hydrocarbons  is  considerable  with  crude  oil  unless  due  at- 
tention is  given  to  the  airing  and  ventilation  of  the  spaces 
where  such  gases  can  collect.  So  long  as  the  spaces  containing 
oil  are  full  there  is  no  danger  of  any  such  trouble,  but  when  they 
are  partially  empty  the  gases  may  collect  in  the  vacant  parts, 
forming  with  the  air  an  explosive  mixture  which  needs  only  a 
spark  or  other  source  of  fire  to  explode  with  violence.  Crude 
oil  residue  does  not  contain  these  lighter  substances  and  is, 
therefore,  safe  from  danger  of  this  character,  though  in  all  cases 
a  due  attention  to  the  matter  of  ventilation  may  be  recom- 
mended. It  may  also  be  noted  that  the  more  dangerous  parts 
of  the  oil  evaporate  with  readiness  under  ordinary  temperatures, 
and  that  crude  oil  exposed  to  the  open  air  rapidly  loses  these 
constituents  and  becomes  thereby  the  safer  for  use.  This  op- 
eration corresponds  to  the  weathering  of  coal,  and  entails,  of 
course,  some  loss,  but  a  loss  the  more  permissible  as  it  makes 
the  fuel  the  safer  to  use. 

[4].  Evaporative  Power. 

Liquid  fuel  has  a  much  higher  evaporative  power  pound 
for  pound  than  coal.  According  to  chemical  analysis  the 
combustion  of  one  pound  of  liquid  fuel  should  liberate 


FUELS.  45 

from  20,000  to  22,000  heat  units,  or  about  one  and  one- 
half  times  as  much  as  good  coal.  This,  combined  with  bet- 
ter efficiency  of  operation  than  with  coal,  has  given  experi- 
mental results  showing  an  evaporative  power  twice  that  of  coal 
or  even  higher.  A  ratio  of  1.7  :  i  or  1.6  :  i,  however,  is  more 
commonly  considered  as  representing  the  average  relation  un- 
der ordinary  conditions,  though  in  some  cases  the  advantage 
has  been  still  less  marked. 


[5].  Stowage  and  Handling. 

The  best  oil  residue  is  of  about  the  same  density  as  sea 
water  or  slightly  heavier.  It  will  thus  run  from  34  to 
35  cu.  ft.  per  ton.  While,  therefore,  its  specific  gravity 
is  less  than  that  of  a  lump  of  coal,  it  stows  much  better, 
so  that  a  given  space  is  capable  of  holding  from  15  to  20 
per  cent  more  fuel  in  the  shape  of  oil  than  in  the  shape 
of  coal.  Combining  this  advantage  with  that  in  evaporative 
power  per  pound,  it  follows  that  the  final  result  is  to  very  nearly 
double  the  capacity  for  steam  generation  per  cubic  foot  of  space 
occupied  by  fuel.  As  a  further  point  it  may  be  mentioned  that 
oil  or  liquid  fuel  may  be  stowed  in  many  places  on  board  ship 
not  available  for  coal  or  for  cargo  in  general.  Such  are  ballast 
tanks,  double  bottoms,  etc.  Again,  the  ease  with  which  oil 
may  be  handled,  flowing  as  it  does  by  gravity  and  stowing  itself, 
is  a  further  point  in  its  favor.  With  proper  facilities  a  ship  may 
be  provided  with  oil  much  more  rapidly  than  with  coal.  It 
should  be  added,  however,  that  oil  refuse  at  a  low  temperature 
may  become  quite  stiff,  flowing  only  sluggishly,  especially  in 
small  pipes.  This  condition  may  require  the  provision  of  spe- 
cial means  for  heating  the  oil  so  as  to  insure  the  necessary  de- 
gree of  fluidity.  Oil  refuse  is,  therefore,  not  a  fuel  suitable  for 
arctic  exploration. 

A  further  advantage  for  liquid  fuel  lies  in  the  great  reduc- 
tion in  the  fireroom  force  which  is  possible  with  its  use.  The 
handling  and  firing  being  practically  automatic,  only  a  few  men 
are  required  to  look  after  the  oil  tanks  and  supply  pipes  in  a  gen- 
eral way,  and  one  fireman  can  give  to  a  large  number  of  furnaces 
the  slight  general  attention  which  they  require.  The  chief 
work  in  the  fireroom  is,  therefore,  reduced  to  water  tending, 
which  remains  as  with  coal. 


46  PRACTICAL  MARINE  ENGINEERING. 

[6],  Use  of  Oil  and  Coal  Combined. 

In  some  cases  the  use  of  oil  in  conjunction  with  coal  has 
given  promise  of  good  results,  especially  on  war  ships,  where  it 
may  be  of  the  utmost  importance  to  be  able  to  very  rapidly  in- 
crease the  power  developed.  In  such  cases  the  coal  would  be 
used  alone  under  ordinary  conditions,  and  oil  added  when  the 
increase  of  power  is  desired.  Experiments  in  the  Italian  Navy 
show  that  for  the  most  complete  combustion  and  best  efficiency 
the  proportion  of  oil  to  coal  should  be  about  one  of  oil  to  five  of 
coal.  In  the  same  manner  as  above  described  the  oil  is  pulver- 
ized and  blown  as  a  spray  into  the  furnaces,  where  it  burns  with 
the  gases  given  off  by  the  coal.  In  this  way  the  oil  furnishes  a 
powerful  resource  for  suddenly  forcing  the  fires  and  increasing 
the  I.  H.  P.  developed,  while  the  amount  of  oil  carried  or  con- 
sumed is  quite  small  compared  with  the  supply  necessary  if  oil 
were  the  only  fuel  used. 

[7].  Cost. 

The  great  drawback  regarding  oil  fuel,  and  one  that 
is  apparently  too  serious  to  be  overcome,  is  that  relat- 
ing to  its  price.  At  ordinary  figures  a  pound  of  steam  would 
now  cost  at  least  as  much  if  generated  by  means  of  oil  as  by 
means  of  coal,  and  if  the  use  of  oil  were  undertaken  by  several 
large  steamship  companies  or  other  large  consumers,  its  price 
would  rise  to  a  point  impossible  at  present  to  foresee.  The  use 
of  liquid  fuel  is  quite  within  the  reach  of  present  engineering 
means,  and  may  be  considered  as  a  mechanical  success.  Due, 
however,  to  the  limited  supply,  and  to  the  uncertainties  regard- 
ing its  price,  its  use  will  probably,  under  present  conditions,  be 
quite  limited  as  a  fuel  for  the  generation  of  steam. 


BOILERS. 


47 


CHAPTER   III. 
BOILERS. 

Sec.  14.    TYPES  OF 

In  the  general  sense,  any  receptacle  in  whioh  steam  is  gen- 
erated by  the  application  of  heat  is  a  boiler.  A  boiler  must, 
therefore,  contain  three  fundamental  features :  a  place  for  the 
fire,  a  place  for  the  water,  and  a  division  or  partition  between 
them.  The  great  variety  of  boilers  arises  from  the  different 


SHELL 

Fig.  9.    Scotch    Boiler. 

forms  which  these  features  take,  and  the  different  manner  in 
which  they  are  arranged.  The  keynote  of  the  development  of 
steam  boilers  from  the  earliest  forms  is  contained  in  the  word 
sub-division;  sub-division  of  the  hot  gases  and  of  the  water  so 
that  no  particle  of  either  shall  be  very  far  from  the  partition  or 
heating  surface,  as  it  is  called.  If  in  addition  to  this  sub-division 
provision  is  made  for  a  definite  flow  of  the  hot  gas  along  one 


48 


PRACTICAL   MARINE   ENGINEERING. 


side  of  the  heating  surface  and  of  the  water  along  the  other  in 
the  opposite  direction,  the  conditions  for  the  most  efficient 
transfer  of  the  heat  of  the  gas  through  the  surface  into  the  water 
will  be  fulfilled.  In  modern  boilers  the  principle  of  sub-division 
has  been  carried  to  a  high  degree  of  development,  but  the  con- 
ditions for  proper  circulation  are  but  imperfectly  fulfilled.  The 


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Fig.  10.     Scotch    Boiler,    End    View. 

sub-division  is  obtained  by  the  use  of  a  large  number  of  tubes 
or  tubular  elements  surrounded  by  a  shell  or  casing.  The  chief 
classification  of  boilers  is  made  according  to  the  relation  of  the 
water  and  hot  gas  to  these  tubular  elements.  If  the  gas  is  led 
through  the  inside  and  the  water  is  on  the  outside,  the  arrange- 
ment is  known  as  a  fire-tube  boiler.  If,  on  the  contrary,  the 


BOILERS. 


49 


gas  is  on  the  outside  and  the  water  circulates  through  the  inside, 
the  arrangement  constitutes  a  water-tube  boiler. 

Fire-tube  boilers  may  be  divided  into  the  Return  tubular  or 
Scotch  boiler,  the  Direct  tubular  or  gunboat  boiler,  the  Locomotive 
boiler,  the  Flue  and  return  tubular  or  leg  boiler,  and  the  Flue  boiler' 


Fig.  11.     Scotch    Boiler,    Longitudinal    Section. 

as  used  on  western  river  steamers.      These  are  illustrated  in 
Figs.  9-14. 

Water-tube  boilers  are  found  in  great  variety,  depending 
on  the  details  of  arrangement  of  the  tubes,  and  drums  or  head- 
ers of  which  they  are  composed.  A  few  representative  types 
are  shown  in  Figs.  15-26.  We  will  first  give  brief  descriptions 


5o  PRACTICAL   MARINE   ENGINEERING. 

of  the  important  features  of  these  boilers,  and  then  take  up  at  a 
later  point  the  subjects  of  their  design  and  construction. 

[i]  The  Scotch  Boiler. 

In  present  practice,  for  marine  purposes,  the  Scotch  boiler 
is  used  more  than  any  other  one  type,  and,  in  fact,  more  than 
all  other  types  combined.  This  boiler,  as  illustrated  in  Figs.  9, 
10,  ii  consists  essentially  of  a  cylindrical  shell  containing  one  or 
more  cylindrical  furnaces,  usually  corrugated  circumferentially 
for  strength,  opening  into  combustion  chambers  at  the  back  end, 
from  which  a  large  number  of  small  tubes  lead  again  to  the  front 
end  or  head  of  the  boiler.  The  grates  are  placed  at  about  the 
center  of  the  height  of  the  furnace,  and  the  fire  and  hot  gases 
occupy  the  upper  part  of  the  furnaces,  the  combustion  cham- 
bers, and  the  inside  of  the  tubes,  while  the  water  and  steam 
fill  all  the  remaining  parts  of  the  shell,  the  water  level  being 
usually  some  6  in.  to  8  in.  above  the  highest  part  of  the  tubes  or 
combustion  chambers.  The  hot  gases  pass  from  the  fire  on  the 
grate-bars  into  the  combustion  chamber,  thence  forward 
through  the  tubes  and  out  through  the  uptake  or  front-connection 
to  the  smoke-stack  or  funnel.  Several  varieties  of  this  boiler  are 
in  common  use.  Thus  the  number  of  furnaces  may  be  one,  two, 
three,  or  four.  They  may  be  fitted  with  separate  combustion 
chambers,  or  there  may  be  one  combustion  chamber  for  all  fur- 
naces, or,  as  is  common  with  four  furnaces,  there  may  be  two 
combustion  chambers — one  for  the  two  furnaces  on  either  side. 
Again,  the  boilers  may  be  single-end  or  double-end.  Fig.  11  is 
an  example  of  the  first.  A  double-end  boiler  consists  of  two 
sets  of  furnaces  opening  from  either  end  of  a  shell  of  double 
length.  It  is  evidently  equivalent  to  a  pair  of  single-end  boilers 
placed  back  to  back  with  the  back  heads  removed  and  the  shells 
joined.  Such  boilers  may  also  have  either  separate  combustion 
chambers  for  each  end,  or  a  common  combustion  chamber  for 
both  ends.  The  former  arrangement  is  to  be  preferred,  and 

becomes  necessary  where  forced  draft  is  used. 

* 
[2]  Direct  Tubular  Boiler,  Gunboat  Type. 

This  boiler  is  rarely  used  except  in  war  ship  practice,  where 
with  low  head  room  it  has  been  occasionally  employed.  It  con- 
sists of  a  shell  with  furnaces  and  combustion  chamber  some- 
what as  in  the  Scotch  boiler,  but  the  tubes,  instead  of  returning 
to  the  front,  fead  on  to  the  farther  head.  To  this  head  is  fitted 


BOILERS.  51 

a  smoke-box  or  uptake  leading  to  the  funnel.  In  such  cases 
the  boiler  for  the  same  power  is  of  smaller  diameter  and  greater 
length  than  the  Scotch  type,  and  it  is  readily  seen  that  the  whole 
arrangement  is  simply  a  mode  of  exchanging  diameter  for 
length. 

[3]  Direct  Tubular  Boiler,  I/ocomotive  Type. 

The  locomotive  type  of  marine  boiler  as  illustrated  in  Fig. 
12  consists  of  a  cylindrical  shell  extended  to  the  front  and  modi- 


Fig.  12.     Locomotive    Type    Boiler. 

fied  in  form  with  flat  sides  and  bottom,  and  flat  or  rounded  top. 
The  furnace  is  of  rectangular  cross-section,  and  is  surrounded 
by  the  shell  at  the  front,  leaving  on  the  sides  a  narrow  space 
known  as  the  water-leg  and  sometimes  a  like  space  underneath 
known  as  the  water  bottom.  The  gases  take  the  same  general 
course  as  in  the  gunboat  type,  the  chief  difference  in  the  two 
being  in  the  form  of  the  furnaces  and  in  the  absence  of  the 
combustion  chamber  in  the  locomotive  type. 

[4]  The  Flue  and  Return  Tubular  or  I/eg  Boiler. 

In  this  boiler,  as  illustrated  in  Fig.  13,  the  hot  gases  pass 
from  the  furnace  through  large  tubes  or  Hues,  as  they  are 
termed,  to  a  combustion  chamber  at  the  farther  end.  They 
then  return  to  the  front  through  small  tubes,  and  are  led  by  an 
appropriate  uptake  to  the  funnel.  The  furnace  is  of  rec- 
tangular cross-section,  and  the  front  end  of  the  boiler  is  modi- 
fied on  the  sides  and  bottom  to  correspond  to  this  form,  as  in 
the  locomotive  type.  Water  legs  are  also  formed  in  the  same 
way  on  the  sides  of  the  furnace,  and  from  this  feature  the  boiler 
receives  its  common  name.  This  form  of  the  front  end  of  the 
boiler  with  flat  sides  and  rounded  top  is  sometimes  known  as  a 
wagon-top.  Very  commonly,  as  shown  in  Fig.  13,  an  attachment 
to  the  shell,  known  as  a  steam  chimney,  surrounds  the  lower  part 


52  PRACTICAL   MARINE   ENGINEERING. 

of  the  funnel,  the  office  of  which  is  to  subject  the  steam  to  the 
drying   and    superheating   effects    of   the    gases    on   their   way 


Fig.  13.     Leg  Boiler. 

through  the  funnel.      Boilers  of  this  type  have  been  used  to  a 
considerable  extent  on  tug  and  river  boats. 

[5]    The  Flue  Boiler. 

In  Western  River  practice  use  is  quite  commonly  made  of 
the  return  flue  boiler  as  illustrated  in  Fig.  14.  This  boiler 
is  externally  fired.  The  flames  and  hot  gases  pass  back  along 
the  outside  of  the  boiler  to  a  back  connection  and  then  enter 
the  flues  and  return  through  them  to  the  front,  and  thence  to 
the  uptake  and  funnel.  Boilers  of  the  locomotive  type,  or 
tubular  fire-box  boilers  as  they  are  often  called,  are  also  used  to* 
a  considerable  extent  in  western  river  practice. 


BOILERS. 


53 


[6]  Water  Tube  Boilers. 

Turning  now  to  this  type,  a  brief  description  will  be  given 
of  the  leading  features,  which  may  be  combined  in  the  greatest 
possible  variety,  thus  giving  the  vast  number  of  forms  of  such 
boilers  on  the  market  at  the  present  time.  To  aid  in  the  descrip- 


Fig.  14.    Return   Flue   Boiler. 

tion  a  few  typical  forms  of  such  boilers  are  shown  in  Figs.  15-26. 
Most  boilers  of  this  type  have  one  or  more  cylindrical 
drums  or  chambers  on  top  and  one  or  more  similar  drums  be- 
low, the  two  sets  of  drums  being  connected  by  sets  of  tubes. 
The  feed  usually  enters  first  the  upper  drum,  frequently  passing 
on  its  way  through  a  coil  heater  in  the  base  of  the  stack  or  top 
of  the  boiler.  It  then  flows  down  certain  of  the  tubes  to  the 
lower  drums.  If  these  tubes  are  of  extra  large  size  and  specially 
intended  for  down  flow,  the  boiler  is  said  to  have  special  down 
flow  or  down  cast  tubes  or  pipes,  as  shown  in  Figs.  15,  16,  17,  18, 
20.  In  some  cases  such  tubes  are  omitted,  and  the  feed  must 
descend  through  part  of  the  small  inner  tubes.  In  any  case, 
after  finding  its  way  to  the  lower  drum  it  enters  the  up  How  or 
steam  forming  tubes,  which  are  surrounded  by  the  hot  gases 
coming  from  the  furnace  below  them.  During  the  passage  of 
the  water  upward  it  is  partly  converted  into  steam,  and  the 
mixture  issues  from  the  upper  end  of  the  tubes  into  the  upper 
drum.  There  the  steam  is  separated  and  led  to  the  engine, 
while  the  water  joins  that  already  in  this  drum,  and  thus  begins 
another  round.  In  some  cases  the  upper  ends  of  the  steam 
forming  or  delivery  tubes  are  below  the  level  of  the  water  in 
the  upper  drum,  and  they  are  then  said  to  be  drowned  or  wet. 
In  other  cases  they  are  above  the  water  level  and  are  said  to 
be  dry.  In  still  other  forms  they  enter  at  about  the  middle  of  the 
drum  or  about  the  water  level,  and  may  be  wet  or  dry  as  the 
level  varies.  See  the  various  cuts  for  examples.  Water  tube 
boilers  are  often  divided  into  two  general  classes :  large  tube  and 


54 


PRACTICAL   MARINE   ENGINEERING. 


BOILERS. 


55 


56  PRACTICAL   MARINE   ENGINEERING. 

small  tube  boilers.  In  the  former  they  are  usually  3  or  4  or 
even  5  in.  dia.,  while  in  the  latter  they  are  usually  from  ij4  to 
\y2  or  2  in.  dia. 

Again,  the  tubular  elements  may  be  made  up  in  a  great 
variety  of  forms.  In  some  they  are  straight,  in  others  curved, 
as  shown  in  the  various  figures.  In  small  tube  boilers  they  are 
very  commonly  curved  or  bent,  while  in  the  large  tube  types 
they  are  straight.  Also  in  some  types  the  elements  are  con- 
tinuous between  drums  or  headers  as  in  Figs.  17,  18,  19,  20, 
while  in  others,  as  in  Figs.  15,  16,  26,  they  are  made  up  of 
lengths  or  of  different  parts  with  screwed  joints,  elbows,  re- 
turns, junction  boxes,  etc.  In  some  they  are  expanded  into  the 
shells  of  the  drums ;  in  others  screwed.  In  some  all  joints  are 
carefully  protected  from  the  direct  action  of  the  flame ;  in 
others  screwed  joints  are  freely  exposed  to  the  flame.  In  some 
the  general  direction  of  the  tubes  is  nearly  horizontal ;  in  others 
nearly  vertical,  and  in  others  bent  or  curved  in  various  forms. 
In  some  types,  as  illustrated  in  Figs.  24,  25,  the  lower  drums  are 
omitted,  or  consist  merely  of  the  lower  portions  of  the  tubes 
and  headers,  or  members  to  which  the  tubes  are  connected.  In 
all  cases  the  grate  lies  below  the  tubes  and  frequently  between 
the  lower  drums,  as  shown  in  the  various  figures,  while  the 
whole  is  surrounded  by  a  casing  intended  to  prevent,  so  far  as 
possible,  the  loss  of  heat  by  radiation. 

[7]  Relative  Advantages  of  Different  Types  of  Boilers. 

For  large  ships  under  ordinary  conditions  and  where  the 
extremes  of  lightness  or  of  speed  on  a  given  displacement  have 
•not  to  be  attained,  the  Scotch  boiler  seems  at  present  to  be 
considered  as  fulfilling  most  satisfactorily  the  all  around  re- 
quirements for  a  marine  boiler,  and  in  consequence  it  is  found 
almost  universally  in  the  mercantile  deep  sea  marine,  as  well  as 
on  the  Great  Lakes,  and  to  a  large  extent  on  inland  craft  of  all 
descriptions,  except  those  of  small  size.  It  is  also  used  to  some 
extent  in  naval  practice,  though  the  use  of  water-tube  boilers 
is  at  the  present  time  extending  quite  rapidly  into  this  field, 
where  their  special  features  become  of  marked  value.  The  pres- 
ent is  a  time  of  change  with  regard  to  types  of  boiler.  It  is 
not  too  much  to  say  that  in  most  of  the  modern  naval  construc- 
tion the  water  tube  boiler  is  accepted  as  the  standard  type  to 
the  exclusion  of  the  fire-tube  boiler.  The  water-tube  boiler 
is  also  making  large  advances  in  the  mercantile  field,  and  not  a 


BOILERS. 


57 


PRACTICAL   MARINE   ENGINEERING. 


BOILERS. 


59 


1 


60  PRACTICAL   MARINE   ENGINEERING. 

few  modern  ships  of  the  mercantile  marine  are  now  equipped 
with  this  type  of  boiler. 

For  tugboats,  river  steamers,  and  a  variety  of  small  craft, 
the  various  types  of  direct  fire-tube  and  flue  boilers  have  been 
much  used.  These  boilers  are  more  readily  adapted  to  a  var- 
iety of  demands  regarding  size,  form  and  arrangement,  and  in 
small  sizes  are  perhaps  more  cheaply  built  than  Scotch  boilers. 
In  many  cases,  however,  the  preference  for  boilers  of  this  type 
has  doubtless  depended  on  local  and  special  conditions  quite  in- 
dependently of  their  relative  value  from  the  engineering  stand- 
point. 

For  fast  yachts,  launches,  all  craft  of  the  torpedo-boat  type, 
and  in  fact  in  all  cases  where  the  highest  speed  is  to  be  attained 
on  the  least  weight,  the  water-tube  boiler  has  become  a  neces- 
sity, and  in  one  or  another  of  its  many  forms  is  universally  em- 
ployed. 

The  weight  of  Scotch  boilers  without  water,  per  square 
foot  of  heating  surface,  is  usually  from  about  25  to  30  Ib. ;  of 
water-tube  boilers  of  the  lighter  types  from  12  to  20  Ib.  The 
weight  of  the  contained  water  per  square  foot  of  heating  surface 
is  usually  from  12  to  15  Ib.  for  Scotch  boilers,  and  from,  say 
1.5  to  3  Ib.  for  water-tube  boilers.  It  results  that  Scotch  boil- 
ers with  water  will  weigh  from,  say,  35  to  50  Ib.  per  square  foot 
of  heating  surface,  while  water-tube  boilers  will  similarly  weigh 
from  13.5  to  23  Ib.  These  figures  are  not  to  be  considered  as 
giving  absolute  limits,  but  simply  as  representative  values  for 
average  types.  It  should  be  noted,  however,  that  a  square  foot 
of  heating  surface  in  a  Scotch  boiler  seems  to  be  somewhat 
more  efficient  than  in  a  water-tube  boiler.  It  is  difficult  to  es- 
timate the  difference  numerically,  but  other  conditions  being 
equal,  it  would  probably  be  safe  to  give  to  the  water-tube  boiler 
additional  heating  surface  to  the  extent  of  from  ten  to  twenty 
per  cent.  On  the  other  hand,  it  must  be  remembered  that 
water-tube  boilers  can  stand  forcing  to  a  much  higher  degree 
than  fire-tube  boilers.  With  the  latter  supplying  steam  to  triple 
expansion  engines  the  ratio  of  heating  surface  to  I.  H.  P.  can 
hardly  be  recluced  below  2,  while  with  the  former  this  ratio  has 
been  reduced  in  many  cases  to  less  than  one  and  one-half,  and, 
as  reported  in  certain  extreme  cases,  to  between  one-half  and 
one.  Water-tube  boilers  have  the  further  advantage  that  they 
are  more  readily  constructed  for  the  higher  and  higher  steam 


BOILERS. 


61 


PRACTICAL   MARINE   ENGINEERING. 


BOILERS. 


64  PRACTICAL   MARINE   ENGINEERING. 

pressure  which  modern  practice  is  continually  demanding. 
With  water-tube  boilers,  due  to  the  construction  and  to  the 
smaller  amount  of  contained  water,  there  is  also  less  danger 
from  disastrous  explosion.  With  water-tube  boilers  steam  may 
be  raised  much  more  quickly  than  with  fire-tube  boilers ;  from 
one-quarter  to  one-half  hour  is  sufficient  with  the  former,  while 
from  three  to  four  hours  should  be  taken  with  the  latter. 

Water-tube  boilers  are  also  much  more  portable  than  fire- 
tube.  In  many  forms  spare  parts  or  even  the  whole  boiler  may 
be  shipped  in  elements  or  sections  across  country  by  rail  or  to 


Fig.  23.     Lagrafel    and    D'Allest    Boiler. 

foreign  ports  by  ship  transport,  put  on  board  the  steamer  for 
which  they  are  intended,  and  erected  in  place  without  difficulty. 
On  the  other  hand,  the  water-tube  boiler  imperatively  re- 
quires fresh  water  feed.  Under  modern  conditions  this  should 
be  provided  no  matter  what  the  type  of  boiler  in  use,  but  if  in 
emergency  salt  water  must  be  used,  the  fire-tube  boiler  will  re- 
ceive the  lesser  injury.  Again,  from  the  small  amount  of  water 
contained  as  a  stock  upon  which  to  draw,  the  water-tube  boiler 
requires  a  more  uniform  feed  than  the  fire-tube  boiler,  and  is 
generally  more  sensitive  to  variations  in  the  conditions  under 
which  it  works.  Again,  the  rupture  of  a  tube  is  a  more  serious 


BOILERS. 


Fig.  24.     Babcock  and  Wilcox  Boiler. 


^"ESCAPE   PIPE  CARRIED  AROUIfO  SMOKE 
PIPE  TO  BE  AFT  OF  IT  ABOVE  UPPtR  OECK 


<>0  55  50  45  40 

Fig.  25.     Arrangement  of  Fireroom  with  Babcock  and  Wilcox  Boilers. 


66 


PRACTICAL   MARINE   ENGINEERING. 


FEED  OUTLET 
PROM  ECONOMISER 


STEAM 
OUTLET 


FEED  INLET  TO  BOILER 
AFTER  LEAVING  •**   ^ 
ECONOMISER 


Fig.  26.     Belleville    Boiler. 


BOILERS.  67 

matter  in  the  water-tube  than  in  the  fire-tube  boiler.  In  the 
latter  it  may  be  plugged  without  disturbing  the  water  and  steam 
in  the  boiler,  and  with  only  a  momentary  interruption  to  its 
operation.  In  the  former  it  is  usually  necessary  to  disconnect 
the  boiler,  draw  the  fires,  blow  down  the  water,  and  plug  or  in- 
sert a  new  tube.  Water-tube  boilers  are  also  not  readily  made 
in  large  sizes  or  units.  Scotch  boilers  may  be  made  in  2,000 
horse  power  units  or  even  larger,  while  half  of  this  or  less  is 
about  the  maximum  for  the  water-tube  boiler.  An  outfit  of  the 
latter  for  large  power  requires,  therefore,  a  large  number  of 
boilers  with  a  corresponding  increase  in  the  fittings  and  attach- 
ments. On  the  other  hand,  the  temporary  removal  of  one 
boiler  for  repair  is  of  less  importance,  as  the  size  is  decreased 
and  number  increased. 

To  summarize  the  general  comparison  between  water-tube 
and  fire-tube  boilers,  the  former  have  relative  advantages  in  the 
following  chief  points :  Weight,  ability  to  stand  forcing,  suit- 
ability for  high  pressures,  greater  safety  from  disastrous  explo- 
sion, and  quickness  of  raising  steam.  On  the  other  hand  they 
have  relative  disadvantages  in  these  points :  A  more  rigid  re- 
striction of  the  feed  to  fresh  water,  the  necessity  of  greater 
regularity  of  feed,  greater  difficulty  in  dealing  with  leaky  tubes, 
and  general  sensitiveness  to  variation  in  the  conditions  of  use, 
to  which  may  be  added  the  present  feeling  of  uncertainty  as  to 
their  durability  and  efficiency  under  the  conditions  prevailing  on 
deep  water  voyages. 

Sec.  15.    RIVETED  JOINTS. 

The  various  joints  in  a  boiler  are  usually  of  the  riveted 
form.  The  use  of  welded  joints  in  various  parts  of  boiler  con- 
struction is  increasing  somewhat  as  greater  skill  is  acquired  in 
making  them,  but  in  ordinary  practice  the  joints  are  riveted,  and 
of  various  types,  as  follows  : 

Riveted  joints  are  divided  into  lap  joints  and  butt  joints, 
according  as  the  plates  lap  over  each  other  (see  Figs.  31-34), 
or  butt  together  at  the  edges,  and  are  covered  by  one  or  two 
butt  straps  (see  Figs.  35-39).  They  are  also  divided  according 
to  the  number  of  rows  of  rivets  into  single,  double  or  triple 
riveted  joints  (see  Figs.  31-33). 

The  rivets  are  usually  staggered  in  arrangement,  as  shown 
in  Figs.  32-39.  Sometimes,  though  rarely,  the  chain  arrange- 


68 


PRACTICAL   MARINE   ENGINEERING. 


ment,  as  shown  in  Fig.  27,  is  used.  While  chain  riveting  is  as 
strong,  or(perhaps  even  slightly  stronger,  than  staggered  rivet- 
ing, the  latter  gives  a  better  disposition  of  rivets  for  making  a 
steam  or  water-tight  joint,  and  this  fact  leads  to  its  more  fre- 
quent use  in  boiler  construction.  In  butt  joints  the  arrange- 
ment of  rivets  is  duplicated  on  each  side  of  the  joint,  and  the 
style  of  riveting  is  named  according  to  the  arrangement  on  one 
side.  Thus,  Fig.  35  shows  a  double-riveted  and  Fig.  36  a  triple- 
riveted  butt  joint. 

A  riveted  joint  may  fail :  (i)  In  the  plate  by  tearing  out  or 
across  from  hole  to  hole,  see  Figs,  28,  29;  (2)  In  the  rivet  by 
shearing;  (3)  in  the  plate  or  rivet  by  a  crushing  of  the  material. 


Fig.  27. 

The  failure  of  a  joint  by  the  tearing  out  of  the  plate  in  front 
of  the  rivet,  as  in  Fig.  29,  is  safely  guarded  against  by  placing 
the  row  of  rivets  at  a  proper  distance  from  the  edge  of  the  plate. 
This,  by  experience,  is  found  to  be  about  one  diameter  in  the 
clear,  or  one  and  one-half  diameters  from  edge  of  plate  to  center 
line  of  rivets.  In  lap  joints  and  butt  joints  with  one  cover,  as 
in  Fig.  30,  the  rivets  resist  shearing  at  one  section  only.  In 
butt  joints  with  double  covers,  as  in  Figs.  35-38,  the  rivets  re- 
sist shearing  at  two  sections.  The  total  shearing  strength  of  a 
rivet  in  double  shear  is  usually  taken  as  somewhat  less  than 
twice  the  strength  in  single  shear.  The  British  Board  of  Trade 
rules  give  ij4  as  the  ratio  to  be  used. 

With  usual  proportions  the  last  mode  of  failure  mentioned 
above  is  the  least  likely  to  occur,  so  that  so  long  as  the  proper 
limits  are  not  exceeded  the  resistance  to  crushing  needs  no  es- 
pecial examination.  These  limits  will  be  given  in  detail  at  a 
later  point. 

The  strength  of  a  riveted  joint  is,  of  course,  determined  by 


BOILERS. 


69 


whichever  is  the  weaker  of  the  two,  the  plate  or  the  rivets.  In 
a  properly  designed  joint  the  strength  of  the  plate  and  that  of 
the  rivets  should  be  equal,  so  that  there  will  be  no  more  likeli- 
hood of  failure  in  one  way  than  the  other.  It  may  be  remarked, 
however,  that  since  corrosion  usually  affects  the  plate  only,  it  is 
often  considered  good  practice  to  give  to  the  plate  a  slight  ex- 


Fig.  28. 


Fig.  29. 


cess  of  strength,  so  that  even  after  some  wasting  by  corrosion 
the  joint  may  still  be  in  fair  proportion  as  to  the  relative 
strength  of  plate  and  rivets.  No  exact  directions  can  be  given 
for  this  increase,  as  it  is  simply  a  matter  of  judgment. 

The  investigation  of  the  strength  of  riveted  joints  by  any 
simple  theory  is  necessarily  quite  imperfect,  because  we  do  not 
know  in  just  what  way  the  stress  is  distributed  through  the  re- 
maining part  of  the  plate,  nor  through  the  section  of  the  rivet, 


Fig.  30. 

nor  what  allowance  to  make  for  the  frictional  grip  of  the  joint. 
The  proportions  given  by  the  following  equations,  however,  are 
those  which  will  give  practically  equal  strength  of  plate  and 
rivets,  using  the  British  Board  of  Trade  rules.  These  rules 
represent  standard  and  reliable  practice,  based  on  wide  experi- 
ence, and  are  substantially  adopted  by  the  United  States  inspec- 
tion authorities.  In  thus  considering  a  joint  we  take  simply 
an  element  such  as  that  between  AB  and  CD  in  the  following 
diagrams.  It  is  clear  in  each  case  that  the  whole  joint  may 
be  considered  as  made  up  of  a  series  of  such  elements  : 


PRACTICAL   MARINE   ENGINEERING. 


Let  p  denote  the pitc h  of  the  rivets  :  that  is,  the  distance  from 

center  to  center.      Where  the  rivets  in  one  row  are 

pitched  twice  as  far  apart  as  in  another  (see  joints 

D,  H,  etc.),  p  denotes  the  larger  of  the  two  values. 

"    d  denote  the  diameter  of  rivet. * 

"    n  =:  p  -r-  d  =  number  of  rivet  diameters  in  the  pitch. 
"    t  =  thickness  of  plate. 
«   a  =  t  +  d. 

"  T  =  tensile  strength  of  plate  per  square  inch  of  section. 
"  S  =  shearing  strength  of  rivet  per  square  inch  of  sec- 
tion. 

The  ratio  of  5  to  T  is  taken  as  23  : 28  or  5"  =  .821  T. 
The  efficiency  of  the  joint  is  the  ratio  between  the  strength 
of  the  joint  and  the  original  strength  of  the  plate.  It  will  be 
seen  by  the  formulae  given  later  that  the  efficiency  of  a  joint  is 
increased  as  d  and  p  are  made  larger.  There  is,  however,  a 
practical  limit  to  the  increase  in  d,  due  to  the  difficulty  of  head- 
ing up  very  large  rivets,  and  a  limit  to  the  increase  in  p,  due  to 
the  necessity  of  guarding  against  leakage.  If  the  general  pro- 
portions between  d  and  /,  as  indicated  later  in  connection  with 
the  various  joints,  are  observed,  the  result  will  be  a  pitch  within 
safe  limits,  and  a  joint  agreeing  well  with  the  best  practice. 

The  largest  permissible  values  of  the  pitch,  according  to 
the  Board  of  Trade  rules,  are  given  by  the  following  formula : 

p  =  Ct  +  if 
where  C  is  drawn  from  the  following  table : 


FORM  OF  JOINT  AS 
SHOWN  BELOW. 

C 

FORM  OF  JOINT  AS 
SHOWN  BELOW 

C 

A    

I    "*! 

F 

463. 

B  

2    62 

G  

5C2 

C    

7   47 

H 

6  oo 

D  

4.  14 

I  

6  oo 

E  

•i    CQ 

In  no  case  should  the  pitch  exceed  10  inches. 
We  will  now  proceed  with  the  equations  and  proportions 
for  various  forms  of  riveted  joints. 


*  Strictly  speaking  the  diameter  of  the  rivet  hole  should  be  used,  as  it  is 
about  1-16  inch  larger  than  the  rivet  before  heading  up.  In  the  Board  of 
Trade  Rules,  however,  the  diameter  of  rivet  is  used.  The  difference  in 
proportion  of  joint  is  quite  small,  and  probably  not  of  practical  importance. 


Joint  A. 


BOILERS. 
Lap  Joint. 


Single  Riveted. 


h 

h 

Q 

Q 

«  —  P  —  i 

E 
Fig.  Z 

r 

1.    Joint 

D                   ' 
A. 

) 


B  3        d 

The  element  is  A  B  D  C,  containing  one  rivet.    We  have  in 
this  case  : 

Strength  of  Plate  =  t  (p  —  d)  T 

Strength  of  Rivet  =  $xd2S 

For  equal  strength  of  plate  and  rivet, 


--or;/=  i  +  -645-7 


Efficiency  = 


n  —  i 


•645 


a  -f-  .645 


The  ratio  d  -r-  t  may  vary  from  1.5  to  2.5,  the  lower  values 
being  more  commonly  employed  with  very  thick*  plates  on  ac- 
count of  the  difficulty  of  heading  up  excessively  large  rivets, 
and  the  necessity  of  a  moderate  pitch  to  insure  against  leakage. 
In  order,  furthermore,  to  guard  against  danger  of  rupture  by 
crushing,  the  upper  limit,  2.5,  should  not  be  exceeded. 

The  foregoing  operations  may  be  expressed  also  by  the 
following : 

Rule,  (i)  Select  a  diameter  of  rivet  according  to  the  thick- 
ness of  the  plate  and  the  directions  given. 

(2)  Multiply  this  diameter  by  .645  and  divide  by  the 

thickness  of  plate. 

(3)  Add  i  to  the  result  obtained  in  (2). 

(4)  Multiply  the  diameter  of  rivet  by  the  result  ob- 

tained in  (3),  and  the  result  will  be  the  pitch 
suited  to  the  diameter  chosen. 


72  PRACTICAL   MARINE   ENGINEERING. 

(5)  Select    the    nearest    working    dimension,    going 

usually  above  in  order  to  give  slight  excess  of 
strength  to  the  plate. 

(6)  To  find  strength  of  plate  in  the  joint,  subtract  the 

diameter  of  rivet  from  the  pitch,  multiply  by 
the  thickness  and  by  the  tensile  strength  per 
square  inch  of  section. 

(7)  To  find  strength  of  rivet,  find  area  of  section, 

multiply  by  the  same  strength  per  square  inch 
as  in  (6),  and  then  by  .821. 

(8)  To  find  original  strength  of  plate  multiply  pitch 

by  thickness  of  plate,  and  by  the  tensile  strength 
per  square  inch,  as  in  (6). 

(9)  To  find  the  efficiency,  divide  the  lower  of  the  two 
results  found  in  (6)  and  (7)  by  that  found  in  (8). 

Example.     To  lay  out  a  single  riveted  lap  joint  for  J/£  inch 
plates,  using  %  inch  rivets. 


Then  7/e  X  .645  -*-*==  7  X  '^  X  '  =  1.13 

O 

And  1.13  +  i.oo  =  2.13. 

And  2.13  X  J  =  1.86  =  pitch. 

Take  the  nearest  eighth  above  and  we  have  pitch  =  i% 
inch. 

Then  taking  strength  of  plate  at  60,000  Ibs.  per  square  inch 
we  have  : 

Strength  of  Plate  in  Joint  =(ij  —  J)  X  -J  X  6,000  =  30,000. 
Area  of  £  inch  rivet  =  .60  sq.  in. 
Strength  of  rivet  =  .60  X  60,000  X  -82!  =  29,550. 
Original  strength  of  plate  =  if  X  -J  X  60,000  =  56,250. 
Efficiency  =  29,550  -f-  56,250  =  .525. 

Similarly,  if  we  should  take  15-16  inch  rivets,  we  should  find 
for  equal  strength  in  plate  and  rivet  a  pitch  of  2.07  inches.  If 
we  take  a  pitch  of  2T/8  inches  we  shall  find  an  efficiency  of  .533. 
If  we  take  the  2.07  exact  the  efficiency  will  be  .548. 


Joint  B. 


BOILERS. 


Lap  Joint. 


Double  Riveted. 


73 


Fig.  32.    Joint    B. 


q  not  less  than  (.  6  /  -|-  .  4  d~} 
Hence  H  not  less  than  y  (i.  i  /  -1-  .4  d)  (.  i  /  -f  .4  d) 


Where  there  are  two  or  more  rows  of  rivets  they  must  be 
placed  at  a  sufficient  distance  apart,  so  that  there  may  be  no 
danger  of  rupture  along  a  zig-zag  line,  as  indicated  in  the  di- 
agram. To  this  end  the  British  Board  of  Trade  rules  give  cer- 
tain values  for  the  distance  q  as  given  above  for  this  case.  This 
distance  is  known  as  the  diagonal  pitch.  The  rules  are  derived 
from  experiment.  The  distances  resulting  may  be  considered 
as  the  smallest  allowable.  In  practice  the  values  of  q  are  often 
made  somewhat  greater  than  would  result  from  the  rules. 
Having  selected  the  distance  q,  the  location  of  the  second  row 
of  rivets  is  easily  found  from  the  first  by  constructing  a  triangle 
with  base  equal  to  />,  and  the  two  other  sides  each  equal  to  q. 

In  this  case  the  element  A  B  D  C   contains  one  whole  rivet 
and  two  halves,  or  two  rivets  in  all.     We  have  then  : 
Strength  of  Plate  —  t  (p  —  d)  T 
Strength  of  Rivets  =  y*7td*S 

For  equal  strength  of  plate  and  rivets  : 


-  -,-  or  n  =  i  +  i.  29  — 


Efficiency  = 


n  —  i 


1.29 


a  -f-  1.29 


The  values  of  d  -.-  t  may  vary  through  about  the  same 
range  as  in  joint  A,  above,  and  for  the  same  reasons  as  there 


74  PRACTICAL   MARINE   ENGINEERING. 

explained.      These    operations    may    be    expressed    by    a    rule 
similar  to  that  for  joint  A,  the  numbered  sections  referring  to 
that  rule  as  given  above : 
Rule: 

(1)  Same  as  for  joint  A. 

(2)  Use  1.29  instead  of  .645. 

(3),  (4),  (5),  (6)  Same  as  for  joint  A. 

(7)  Take  twice  the  strength  of  one  rivet,  found  as  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  double  riveted  lap-joint  for  y2  inch 
plates,  using  J4  inch  rivets. 

Then  %  X  1.29  •*-  %  =3  X  1''9X  2=  1-935 

4 

And  1.935  +  LOO  =  2.935. 

And  2.935  X  f  =  2.201  =  pitch. 

Taking  the  nearest  eighth  above  we  have  p  =  2^4  inches. 

Then  taking  strength  of  plate  at  60,000,  we  have : 

Strength  of  plate  in  joint  =  (2j  -  -  f )  X  i  X  60,000  = 
45,000. 

Area  of  J4  mcn  rivet  =  .4418  sq.  in. 

Strength  of  rivets  =  .4418  X  2  X  60,000  X  -821  =  43,520. 

Original  strength  of  plate  =  2.\  X  4  X  60,000  =  67,500. 

Efficiency  =  43,520  -f-  67,500  =  .645. 

Similarly  with  %  inch  rivets,  pitched  2%  inches,  the 
strength  of  plate  and  rivets  will  be  nearly  equal,  and  the  effi- 
ciency will  rise  to  .687. 


Joint  C.  Lap  Joint.  Triple  Riveted. 

h  =  a  d 

q  not  less  than  (.6/  -}-  .4^) 


Hence  //"not  less  than  y  (i.  i  /  -f  .4  </)  (.  i  />  -f  .4  <^) 
B  =  3  rf  +  2  // 

In  this  case  the  element  A  B  D  C  contains  two  whole  rivets 
and  two  halves,  or  three  rivets  in  all.     We  have  then : 

Strength  of  Plate  —  t  (p  —  d)  T 

Strength  of  Rivets  —  %nd*S 
For  equal  strength  of  plate  and  rivets : 


BOILERS. 


P  d 

-—or  n  =  i  -r-  1.935— 


75 


"R  flfi  r*  i  i^n  r»\7 

?35 

^_                               AC 

-935 

t 

P 

11                                                      Q' 
/~ 

t 

i  C 

•**• 

\ 

--^7-              0                   ®                   ^ 

B  r 

H                         XQv         /\ 

*«s, 

r 

11 

h 

i  U 

i 

11 

;«.__    p   ^ 

I 

Fig.  33.    Joint    C. 

The  values  of  d  -r-  t  may  vary  through  about  the  same 
range  as  in  joint  A,  above,  and  for  the  same  reasons  as  there 
explained.  These  operations  may  be  expressed  by  a  rule  sim- 
ilar to  that  for  joint  A,  the  numbered  sections  referring  to  that 
rule  as  given  above. 
Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  1.935  instead  of  .645. 

(3),  (4),  (5),  (6)  Same  as  for  joint  A. 

(7)  Take  three  times  the  strength  of  one  rivet  found  as  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  triple-riveted  lap-joint  for  y2  inch 
plates,  using  1/4  inch  rivets. 

3  X  1-935  X  2 


Then  ^  X  i-935 


=2.903 


And  2.903  -h  i. oo  =  3.903. 

And  3.903  X  f  =  2.93  inches  =  pitch. 

Take  p  =  3  inches. 

Then  taking  strength  of  plate  at  60,000,  we  have : 

Strength  of  plate  in  joint  =  (3  —  3)  X  i  X  60,000  =  67,500. 

Area  of  ?4  inch  rivet  =  .4418. 

Strength  of  rivets  =  .4418  X  3  X  60,000  X  -821  ==  65,280. 

Original  strength  of  plate  —  3  X  £  X  60,000  =  90,000. 

Efficiency  =  65,280  -f-  90,000  —  .725. 


PRACTICAL   MARINE   ENGINEERING. 


Similarly  with  %  inch  rivets,  pitched  3%  inches,  the  effi- 
ciency becomes  .764. 


Joint  D.  Lap  Joint, 

inner  row  spaced  one-half  p. 


Triple  Riveted,  with  rivets  in 


h 

-4- 

H 

"I"1 

H 

-•i- 


mi 
II 


a^St/7/ 
_.^5? 


Fig.  34.    Joint    D. 


h  = 


q  not  less  than  (.$/  +  d) 
Hence  H  not  less  than  -\/  (.  5  5  /  -f  d}  (.  05  p  -\-  d) 

B  =  3  d  +  2  H 

As  seen  below,  the  efficiency  of  this  joint  is  superior  to  that 
of  joint  c,  but  it  is  perhaps  slightly  inferior  as  regards  tightness 
against  leakage.  We  have  in  this  case : 

Strength  of  Plate  —  t  (p  —  d)  T 
Strength  of  Rivets  =  xd2  S 
For  equal  strength  of  plate  and  rivets : 

P 


or  n 


Efficiency  = 


n  —  i 


2.58 


a  +  2.58 

The  values  of  d  -T-  t  may  vary  through  about  the  same 
range  as  in  joint  A  above,  and  for  the  same  reasons  as  there 
explained.  These  operations  may  be  expressed  by  a  rule  sim- 
ilar to  that  for  joint  A,  the  numbered  sections  referring  to  that 
rule  as  given  above. 
Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  2.58  instead  of  .645. 

(3)i  (4),  (5)»  (6)  Same  as  for  joint  A. 


BOILERS.  77 

(7)  Take  four  times  the  strength  of  one  rivet  found  as  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  triple-riveted  joint  as  in  D  for  l/2 
inch  plates,  using  %  inch  rivets. 

Then  %  X  2.58  ±  %  =3J<  2-5*  X  2=  ^ 

4 

And  3.87  +  i. oo  =    4.87. 

And  4.87  X  t  =  3.65  inches  =  pitch. 

Take  p  =  3  11-16  inches. 

Then  £  />  =  i  27-32  inches. 

Then  taking  strength  of  plate  at  60,000  we  have : 

Strength  of  plate  in  joint  =  (3-£---  J)  X  i  X  60,000  = 
88,125. 

Area  of  f  inch  rivet  =  .4418. 

Strength  of  rivets  =  .4418  X  4  X  60,000  X  -821  =.  87,050. 

Original  strength  of  plate  —  3-£-X  i  X  60,000  =  110,625. 

Efficiency  =  87,050  -r-  110,625  =  .787. 

With  %  inch  rivets  spaced  2  7-16  inches  in  the  middle  row 
and  4%  in  the  outer  rows,  the  strength  of  plate  and  rivets 
would  be  nearly  equal,  and  the  efficiency  would  rise  to  .81. 

Joint  E.        Double  Butt-Straps.        Double  Riveted, 
h  =  ij  d 
q  not  less  than  (.6  p  -f-  .4  d) 


Hence  //"not  less  than  j/  (i.  i  /  4.  .4  d)  (.  i  /  -j-  .4  d) 
B  =  6  d  +  2  H. 

Thickness  of  each  butt-strap  not  less  than  ^  the  thickness 
of  plate. 

The  arrangement  of  rivets  is  duplicated  on  either  side  of 
the  joint  line  P  Q.  We  need  only  to  investigate  the  part  of  the 
joint  on  one  side  of  P  Q.  The  element  is  then  A  B  D  C,  as  in 
joint  B,  except  that  the  rivets  are  in  double  shear  instead  of 
single  shear.  For  the  total  shearing  strength  of  a  rivet  in 
double  shear,  as  previously  explained,  it  is  customary  to  take 
1 24  times  the  strength  for  single  shear  instead  of  2  times,  or  to 
take  the  two  strengths  in  the  ratio  7  :  4. 

We  then  have : 

Strength  of  Plate  —  t  (p  —  d)  T 
Strength  of  Rh'cts  =  Ind'S 


PRACTICAL   MARINE   ENGINEERING. 
For  equal  strength  of  plate  and  rivets : 

-^-or  ;/  =  i  4-  2.26-— 
d  t 

n  —  i          2.26 


Efficiency 


2.26 


I 


If 


^ 


Fig.  35.    Joint    E. 

In  all  double  butt-strap  joints  d  -i-  /  usually  varies  from  i 
to  ij4-  The  lower  range  of  values,  as  compared  with  joints  in 
which  the  rivets  are  in  single  shear,  is  required  in  order  to  in- 
sure the  joint  against  danger  of  failure  by  crushing. 

These  operations  may  be  expressed  by  a  rule  similar  to  that 
for  joint  A,  the  numbered  sections  referring  to  that  rule  as 
given  above. 
Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  2.26  instead  of  .645. 

(3)>  (4)»  (5)»  (6)  Same  as  for  joint  A. 

(7)  Take  35^  times  the  strength  of  one  rivet,  as  found  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  joint  as  in  E  for  I  inch  plates,  using 
ij/s  inch  rivets. 

Then  ij  X  2.26  -5-  i  =  9X2'26=2.54. 

o 

And  2.54  +  i  =  3.54. 

And  3.54  X-f-==  3.98  inches  =  pitch. 

Take  pitch  =  4  inches. 


BOILERS. 


79 


Then  taking  strength  of  plate  at  60,000  Ibs.,  as  before,  we 
have: 

Strength  of  plate  in  joint  =  (4  -  -  ij)  X  I  X  60,000  — 
172.500. 

Area  of  i-J  inch  rivet  —  -994- 

Strength  of  rivets  =  .994  X  3i  X  60,000  X  ,821  =  171,350. 

Original  strength  of  plate  =  4  X  i  X  60,000  =  240,000. 

Efficiency  =  171,350  -=-  240,000  =  .714. 

Similarly  with  i  inch  plates  and  \l/\  inch  rivets,  pitched 
4^4  inches,  the  strength  of  plate  and  rivets  will  be  about  the 
same,  and  the  efficiency  is  .737. 


oint  F.         Double  Butt-Straps.          7 

>/>/<•  R 

'/ 

z/^ 

I 

n        n        n 

c 

'/f 

1 

1 

^                ^                ^                ^ 

_A__                 ..C 

c 

J 

-- 

-, 

i 

q'           H 

B 

c 

i 

^ 

1 

^g             .  -^  .^.                       ^                        ^ 

q              H 
h 

c 

i 

1 

11 

1 

• 

Fig.    36.    Joint    F. 
k  —    Ij  d 

q  not  less  than  (.6  p  -f-  .4  d) 

Hence  H   "     "      "     i/(i.i/ +  .4  </)  (.i/  + .4^) 
B  =  6  d  +  4  H. 

Thickness  of  each  butt-strap  not  less  than  ^  the  thickness 
of  plate. 

The  element:  of  the  joint  is  A  B  D  C,  as  in  joint  C,  except 
that  the  rivets  are  in  double  shear.  Taking,  as  before,  the 


8o  PRACTICAL   MARINE   ENGINEERING. 

strength  in  double  shear  to  that  in  single  in  the  ratio  7   :  4,  we 
have : 

Strength  of  Plate  =  t  (p  —  d)  T 

Strength  of  Rivets  —  -**.•  rcd~  S 

For  equal  strength  of  plate  and  rivets : 

d 

i  +  3-39 

n  —  i         3-39 


-^-  or  n  =  i  +  3-39 -y 


Efficiency  =• 


3-39 


In  this  joint  d  -±-  t  usually  varies  from  I  to  ij4,  as  explained 
for  joint  E.  These  operations  may  be  expressed  by  a  rule 
similar  to  that  for  joint  A,  the  numbered  sections  referring  to 
that  rule  as  given  above. 

Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  3.39  instead  of  .645. 

(3)>  (4),  (5),  (6)  Same  as  for  joint  A. 

(7)  Take  ^/\  times  the  strength  of  one  rivet,  as  found  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  joint  as  in  F  with  I  inch  plates , 
using  i  3-16  inch  rivets. 


Then  i  -i.  X  3-39  -  i  = 


And  4.03  +  i  =  5.03. 
And  5.03  X  I-|-=  5-97  inches  =  pitch. 
Take  pitch  =  6  inches. 

Then  with  strength  of  plate  at  60,000,  as  before,  we  have : 
Strength  of  plate  in  joint  =  (6  -  -  i-^-)  X   i   X  60,000  = 
288,750. 

Area  of  i-3-inch  rivet  =  1.108. 

16 

Strength  of  rivets  =  1.108  X  5l  X  60,000  X  -821  =286,500. 
Original  strength  of  plate  —  6  X  i  X  60,000  =  360,000. 
Efficiency  =  286,500  -f-  360,000  =  .796. 


BOILERS. 
Joint  G.         Double  Butt-Straps.         Rivets  as  in  Joint  D. 


81 


c: 
c 


d 


;     g 

IP 


I 

I 


1 


Fig.  37.    Joint    G. 
A  =    Ij  rf 

<7  not  less  than  (.3  />  -f  </) 

Hence;/"     "      "     v  (-S5/ +  <0  (.<>5/ +  <0 

5  =  6  rf  +  4  //. 

Butt-straps  to  be  of  thickness  not  less  than  as  given  by  the 
formula : 

Thickness  of  strap  == g5,      ~  ,   X  (thickness  of  plate) 

5  (/ — 2ft) 

The  element  of  the  joint  is  A  B  D  C,  as  in  joint  Z),  except 
that  the  rivets  are  in  double  shear.  Taking,  as  before,  the 
strength  in  double  shear  to  that  in  single  shear  in  the  ratio  7  :  4, 
we  have : 

Strength  of  Plate  —  t  (p  —  d)  T 
Strength  of  Rivets  =^-nd2S 
.  For  equal  strength  of  plate  and  rivets : 


Aor  „ 


+  4-52— 


Efficiency  = 


52 


82  PRACTICAL   MARINE   ENGINEERING. 

In  this  joint  d  -f-  t  usually  varies  from  about  I  to  ij4,  as 
explained  for  joint  E.  These  operations  may  be  expressed  by 
a  rule  similar  to  that  for  joint  A,  the  numbered  sections  re- 
ferring to  that  rule  as  given  above. 

Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  4.52  instead  of  .645. 

(3),  (4),  (5),  (6)  Same  as  for  joint  A. 

(7)  Take  7  times  the  strength  of  one  rivet,  as  found  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  joint  as  in  G  with  il/2  inch  plates, 
using  i^i  inch  rivets. 

Then  ,|  X  4.52  -H  ii  =  I3  X  */'  X-'-  4-9 

°  X  3 

And  4.9  +  i  =  5.9. 

And  5.9  X  i  f  =  9-6  inches  =  pitch. 

Take  pitch  for  outer  rows  9^3  and  for  inner  rows  4-||- 

Then,  with  strength  of  plate  at  60,000,  we  have : 

Strength  of  plate  in  joint  =  (9f  -  -  i J)  X  ij  X  60,000  = 

731^50- 

Area  of  iJ/£  inch  rivet  =  2.074. 

Strength  of  rivets  =  2.074  X  7  X  60,000  X  -821  =  715,200. 
Original  strength  of  plate  =  9!  X  ij  X  60,000  =  866,250. 
Efficiency  =  715,200  -r-  866,250  =  .826. 

Joint  H.          Double  Butt-Straps.  Triple   Riveted,   with 

double  spacing  in  outer  row  on  each  side. 

h  =  ij  d 
q  not  less  than  .3  p  -f-  .4  d 

g,  "    "     "    -3/  +  ^ 


Hence  H  «  ^(.55  p  +  .4^)  (.05  />  +  .4 


Thickness  of  butt-straps  found  by  same  formula  as  for 
joint  G. 

The  element  of  the  joint  is  A  B  DC,  containing  four  whole 
rivets  and  two  halves,  or  five  in  all.  These  are  all  in  double 


BOILERS. 


shear.     Taking,  as  before,  the  strength  in  double  shear  to  that 
in  single  in  the  ratio  7  :  4,  we  have : 

Strength  of  Plate  =  t  (p  —  d)  T 

Strength  of  Rivets  =  -2|_;r  d2  S 
For  equal  strength  of  plate  and  rivets : 

p  d 

-^-or«=  i  +  5.64  — 


Efficiency 


n  —  i          5.64 
n      ~  a  4.  5.64 


h 

't 
H 

--*< 

H, 

m- 

h 


p 


Fig.  38.    Joint  H. 

In  this  joint  d-±-  t  usually  varies  from  i  to  i%,  as  explained 
for  joint  E.     These  operations  may  be  expressed  by  a  rule  sim- 
ilar to  that  for  joint  A,  the  numbered  sections  referring  to  that 
rule  as  given  above. 
Rule : 

(1)  Same  as  for  joint  A. 

(2)  Use  5.64  instead  of  .645. 

(3).  (4),  (5)»  (6)  Same  as  for  J°int  A- 

(7)  Take  8^4  times  the  strength  of  one  rivet,  as  found  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  joint  as  in  H  with  i^J  inch  plates, 
using  I  7-16  inch  rivets. 


84  PRACTICAL  MARINE  ENGINEERING. 


And  5.9  +  i  =  6.9. 

And  6.9.  +  i  -^-=  9.92  inches  =.  pitch. 

The  limiting  pitch  by  the.  Board  of  Trade  rule  for  this  case 
would  be  9.87.  This  means  that  a  pitch  of  9.92  or  larger  would 
not  be  passed  without  special  permission.  If  necessary  to  re- 
duce below  the  limit,  the  joint  should  be  re-designed  with  a 
smaller  rivet.  This  case  illustrates  the  point  that  these  limiting 
values  of  the  pitch,  if  rigidly  adhered  to,  would  prevent  the  at- 
tainment of  the  best  joint  efficiencies  with  thick  plates.  We 
shall  here  assume  the  right  to  proceed  with  the  pitch  derived 
from  the  formula  which  we  will  take  as  10  inches  for  the  outer 
and  5  inches  for  the  inner  rows. 

Then  taking  strength  of  plate  at  60,000  we  have  : 

Strength  of  plate  in  joint  =  (10--  i-£)  X  if  X  60,000  = 
706,400. 

Area  of  i-£-  inch  rivet  =  1.623. 

Strength  of  rivets  =  1.623  X  8f  X  60,000  X  -821  =699,600. 

Original  strength  of  plate  =  10  X  if  X  60,000  =  825,000. 

Efficiency  =  699,600  -r-  825,000  =  .848. 

Joint  I.  Double  Butt-Straps.  Triple  Riveted,  outer  row 
on  each  side  being  double  spaced,  and  passing  through  inside  butt- 
strap  only. 

h=i$d 
q  not  less  than  .3  p  +  -4  d 


_ 
Hence  H  "      "      "     T/  (.55  p  +  .4  d  )  (.05^  +  .4  d) 

11      #i"       "      "     i/(-55/  +  ^)(-o5/  +  ^) 
B=6d+  2  H 

£,=  64+  2  H+  2  H, 

Thickness  of  butt-straps  found  by  same  formula  as  for  joint 
G.  The  element  of  this  joint  is  A  B  D  C,  with  four  rivets  in 
double  shear  and  one  in  single  shear.  Taking,  as  before,  the 
strength  in  double  shear  to  that  in  single  in  the  ratio  7  :  4,  we 
have: 

Strength  of  Plate  —  t  (p  —  d)  T 
Strength  of  Rivets  =  2  xd2  S 
For  equal  strength  of  plate  and  rivets,  we  have  : 


BOILERS. 


85 


/  <:   d 

-^-  or;/=i  -f  5.16  — 


Efficienc 

"  —  i         5.16 

«          a  4-  5- 

16 

t 
•  [ 

^   B, 
* 

1 

E 

®          ® 

P                                            A                                 CO 

H         q 

H,  i             "q, 

\*m 

1 

fr 

• 

(.--           _.n__      --H, 

t 

1 

!  ( 

1 

i 

^ 

> 

k 

\ 

I 

:( 

i     \ 
B, 

I 

11 

c 

\ 

1 

1 

^ 
f 

I 

+ 

1' 

1 

1 

^ 

Fig.  39.    Joint    I. 

In  this  joint  d  -f-  t  usually  varies  from  I  to  1^4,  as  explained 
for  joint  E.     These  operations  may  be  expressed  by  a  rule  sim- 
ilar to  that  for  joint  A,  the  numbered  sections  referring  to  that 
rule  as  given  above. 
Rule: 

(1)  Same  as  for  joint  A. 

(2)  Use  5.16  instead  of  .645. 

(3)>  (4),  (5),  (6)  Same  as  for  joint  A. 

(7)  Take  8  times  the  strength  of  one  rivet,  as  found  for 
joint  A. 

(8),  (9)  Same  as  for  joint  A. 

Example.  To  lay  out  a  joint  as  in  I  with  i^  inch  plates, 
using  i  7-16  inch  rivets. 


Then  i-£-  x  5>l6  -^ 


23x5.16x8 
16        ii 


o 


And  5.40  +  J  =  6.40. 

And  6.40  X  i  -^-=  9-2  inches  =  pitch. 


86  PRACTICAL   MARINE   ENGINEERING. 

We  will  take  9^  for  pitch  of  outer  row,  and  hence  4^  for 
pitch  of  inner  rows.  Then,  taking  strength  of  plate  at  60,000, 
we  have : 

Strength  of  plate  in  joint  =  (9^  —  l^-)  X  if  X  60,000  = 

644,530. 

Area  of  i-^-  inch  rivet  —  1.623. 

Strength  of  rivets  =  1.623  X  8  X  60,000  X  -821  =  639,600. 

Original  strength  of  plate  =  9J  X  if  X  60,000  =  763,125. 

Efficiency  =  639,600  -f-  763,125  =  .838. 

An  examination  of  the  values  of  the  efficiency  will  show 
that  these  various  joints  for  the  same  value  of  d  ~-  t  stand,  in 
this  respect,  in  the  order : 

H,  I,  G,  F,  D,  E,  C,  B,  A. 

Sec.  16.    MATERIALS  AND  CONSTRUCTION. 

[i]   Materials. 

Open  hearth  mild  steel  is  used  almost  universally  as  the 
material  for  boiler  construction,  and  in  standard  practice  is  used 
exclusively  for  shells,  drums,  heads,  furnaces,  combustion 
chambers  and  braces.  Both  steel  and  wrought  iron  are  used 
for  tubes,  though  solid  drawn  steel  tubes  may  be  considered  as 
the  better  representing  advanced  engineering  practice. 
Wrought  iron  is  also  used  to  some  extent  for  rivets,  though  in 
the  best  modern  practice  steel  rivets  are  preferred. 

[2]  Joints. 

The  various  plates  of  a  boiler  are  fastened  together  by 
riveted  joints.  These  are  of  several  varieties,  as  discussed  in 
Sec.  15,  and  to  which  reference  may  be  made. 

The  holes  in  the  plates  are  either  drilled  or  punched.  The 
former  method  is  much  the  better.  In  the  operation  of  punch- 
ing, a  thin  skin  of  metal  about  the  hole  is  so  severely  strained 
that  its  strength,  and  especially  its  ductility  and  toughness,  are 
reduced  far  below  what  they  are  in  the  remainder  of  the  plate. 
This  is  not  the  case  with  the  operation  of  drilling,  or,  at  least, 
not  to  anything  like  the  same  extent.  Drilled  holes  may  also 
be  located  more  accurately  than  punched  holes,  and  thus  with 
the  former  the  parts  of  a  riveted  joint  may  be  more  perfectly 
fitted  than  with  the  latter.  The  operation  of  drilling  leaves, 


BOILERS.  87 

however,  a  sharp  edge,  which  should  be  removed  by  a  reamer  in 
order  to  avoid  any  tendency  to  cut  the  rivet.  In  spite  of  the 
greater  cost  of  drilled  holes  they  are  now  generally  accepted  as 
the  best  for  all  high-class  work,  and  in  many  specifications  no 
holes  are  allowed  to  be  punched. 

Riveting  is  either  by  hand  or  by  machine ;  usually  hy- 
draulic. The  latter  gives  much  the  better  result,  and  is  pre- 
ferred where  the  machine  can  be  made  available.  In  many 
cases  the  construction  is  such  that  the  jaws  of  the  machine 
cannot  be  brought  to  bear  on  the  joint,  and  in  consequence  hand 
riveting  must  be  employed. 

After  being  riveted  the  joints  are  calked  to  insure  tightness 
against  leakage.  This  operation  consists  in  beating  down  the 
edges  of  the  metal  against  the  face  of  the  opposite  plate  by 
means  of  special  pneumatic  driven  or  hand  tools,  as  shown  in 
Fig.  40.  These  are  known  as  calking  tools,  and  are  of  two 


\ 

\ 

\ 

Fig.  40.     Calking   Tools. 

types,  square  and  round  nosed,  as  shown  in  the  figure.  The 
latter  form  is  usually  employed  in  modern  practice.  For  op- 
erations on  board  ship  the  common  hand  tool  is,  of  course, 
most  commonly  used ;  but  for  extensive  calking,  as  in  the  con- 
struction of  boilers  in  the  shop  and  where  compressed  air  is 
available,  the  pneumatic  driven  tool  is  very  largely  displacing 
the  hand  tool. 

[3]  Construction  of  Fire-Tube  Boilers. 

We  will  now  consider  the  chief  features  of  the  construction 
of  a  Scotch  boiler.  This  will,  at  the  same  time,  sufficiently  il- 
lustrate the  operations  involved  in  the  construction  of  other 
types  of  fire-tube  boilers. 

In  the  best  practice  the  longitudinal  joints  are  double  butt- 
strapped  and  triple-riveted  in  order  to  give  to  the  boiler  in  this 
direction  the  highest  possible  proportion  of  the  strength  of  the 
plate  itself.  The  circumferential  joints,  those  which  run  around 
the  shell,  are  lapped  and  double  or  triple  riveted.  So  far  as  in- 


88 


PRACTICAL   MARINE   ENGINEERING. 


ternal  pressure  is  concerned  the  boiler  is  twice  as  strong  to  re- 
sist rupture  around  the  girth  as  lengthwise  so  that  a  lapped  cir- 
cumferential or  girth  joint  is  quite  enough  for  strength  alone, 
and  it  only  remains  to  make  it  steam  and  water  tight  and  to  in- 
sure the  necessary  stiffness  of  the  boiler  as  a  whole.  (See  Sec. 
63.)  Single-ended  boilers  are  usually  made  with  two  courses 
of  plates,  as  in  Fig.  n.  Double-ended  boilers  are  usually  made 
with  three  courses.  Each  course  consists  of  two  or  three 
sheets,  varying  with  the  diameter  of  the  boiler.  The  heads  are 
flanged,  as  shown  in  Fig.  u,  and  thus  secured  by  riveting  to  the 
shell.  In  some  cases  the  shell  has  been  flanged  instead  of  the 
head,  but  such  form  of  construction  is  rare.  The  head  flanges 
are  sometimes  turned  out,  and  sometimes  in,  as  shown  by  the 
figure.  Where  machine  riveting  is  to  be  used  they  must  be 
turned  out  in  order  to  allow  the  riveter  to  do  its  work.  The 
back  head  is  made  usually  in  two  pieces,  with  double  or  triple- 


— Fox. 


— Purves. 


— Morrison. 


Fig.  41.    Styles  of  Corrugation. 


riveted  lap  joints.  The  front  head  is  made  in  two  or  three 
pieces,  according  to  size  of  boiler,  usually  with  double-riveted 
lap  joints. 

The  furnaces,  as  shown,  are  corrugated  in  order  to  give 
greater  strength  and  elasticity.  There  are  three  styles  of  cor- 
rugation in  common  use,  as  shown  in  Fig.  41.  The  furnaces  are 
riveted  to  flanges  formed  on  the  front  furnace  sheet,  and  are 
connected  by  flanging  to  the  sheets  of  the  combustion  chamber. 
Several  different  modes  of  connection  are  in  use  for  this  pur- 
pose. In  one  the  furnace  end  is  left  plain  and  the  flange  is  all 
on  the  combustion  chamber  sheet,  as  in  Fig.  9.  In  another  the 
combustion  chamber  sheets  are  left  plain  and  the  flange  is  on 
the  furnace,  as  shown  in  Figs,  u,  42,  44.  In  some  forms  pro- 
vision is  made  for  removal  and  renewal  without  disturbing  the 
furnace  head  sheets.  Thus,  in  Fig.  9  the  diameter  at  the  front 


BOILERS. 


is  the  same  as,  or  slightly  larger,  than  that  on  the  outside  of 
the  corrugations,  and  so  the  furnace  may  be  withdrawn  through 
the  opening  in  the  front  sheet.  In  other  forms  of  connection, 
where  the  furnace  is  flanged,  especial  provision  must  be  made 
for  removal,  as  shown  in  Fig.  43. 

Here  the  back  end  of  the  furnace  is  necked  in  on  the  bot- 
tom and  sides,  and  a  flange  is  thus  obtained  which  only  extends 
outside  the  outer  diameter  of  the  corrugation  at  the  top.  This 


Fig.  42.     Flanged    Furnace. 

flange  serves  to  attach  the  furnace  to  the  combustion  chamber, 
and  on  cutting  the  joint  loose  the  furnace  may  be  taken  straight 
to  the  front  until  the  upper  flange  strikes  the  front  sheet,  and 
then  swung  upward  and  out  of  the  front  opening,  as  may  be 
readily  seen. 

In  some  cases  where  it  is  difficult  to  obtain  the  necessary 
room  on  the  front  head  for  the  greater  diameter  of  the  outside 


Fig.  43.     Removable  Furnace. 

of  the  corrugation,  or  where,  for  other  reasons,  it  is  not  con- 
sidered preferable  to  have  the  furnaces  removable  without  dis- 
turbing the  front  sheet,  the  furnace  end  at  the  front  runs  out  on 
the  smaller  diameter,  as  shown  in  Fig.  44.  Some  one  of  the 
forms  favoring  easy  removal  may  be  recommended  as  prefer- 
able in  all  ordinary  cases. 

The  combustion  chamber,  as  shown,  is  built  up  of  steel 
plates  flanged  and  riveted  together.      The  details  of  the  con- 


PRACTICAL   MARINE   ENGINEERING. 


stniction  vary  somewhat  with  the  form  of  furnace  attachment 
adopted,  with  the  size  of  the  boiler,  and  with  the  choice  of  the 
designer.  The  front  plate  is  known  as  the  back  tube  sheet.  The 
top  of  the  combustion  chamber  is  sometimes  flat,  as  in  Figs.  9, 
65,  and  sometimes  rounded  up,  as  in  Figs,  n  and  45. 


Fig.  44.     Non-Removable    Furnace. 

The  tubes  are  secured  into  the  tube  sheets  by  "expanding," 
and  "beading"  or  turning  over  at  the  back  or  at  both  the  back 
and  front  ends.  See  Figs.  46,  47,  48.  Tubes  are  expanded  by 
means  of  a  tool  as  shown  in  Fig.  49,  representing  the  Dudgeon 
expander.  The  tool  is  introduced  into  the  mouth  of  the  tube 
and  the  small  steel  rolls  are  forced  out  by  means  of  the  tapering 
steel  mandrel  on  which  they  rest.  The  mandrel  is  then  turned 


Fig.  45.    Rounded  Top  Combustion  Chamber. 

around,  and  this  by  means  of  the  frictional  contact  with  the  rolls 
causes  them  to  turn  also,  and  thus  to  roll  around  on  the  inner 
surface  of  the  tube,  carrying  the  whole  tool  slowly  round  and 
round.  The  mandrel  is  continually  forced  in  and  thus  the  rolls 
are  forced  otitward  against  the  tube.  The  action  is  thus  a  roll- 


BOILERS. 


ing  of  the  tube  out  against  the  tube  sheet,  and  in  this  way  the 
joint  is  made  thoroughly  tight. 

The  Prosser  expander,  which  was  generally  employed  in 
former  years,  is  now  but  rarely  used.      It  consists,  as  shown  in 


Fig.  47.    Tube  End. 


Fig.  46.    Tube  End. 

Fig  50,  of  a  hollow  tapering  plug  divided  up  into  separate  ele- 
ments or  sections  which  are  held  together  by  a  steel  band. 
These  are  forced  outward  against  the  inner  surface  of  the  tube 
by  driving  a. taper  mandrel  into  the  hollow  between  the  ele- 


Fig.  48.    Tube  Ends. 

ments.  The  action  of  the  expander  is  thus  to  force  the  metal 
of  the  tube  out  against  the  edges  of  the  sheet  in  a  form  of  cir- 
cular ridge  as  shown  in  Fig.  46. 

Beading  over  the  tube  ends  is  usually  done  with  a  tool,  as 


Fig.  49.     Roller    Tube    Expander. 

shown  in  Fig.  51,  and  the  result  is  as  shown  in  Figs.  46-48.  In 
some  cases  the  tube  sheet  is  recessed  out  for  the  beaded  end  of 
the  tube,  as  shown  in  Fig.  47.  The  front  ends  of  the  tubes,  as 
shown  in  Fig.  48,  are  usually  swelled  slightly  larger  than  the  rear 
ends  to  facilitate  removal.  The  thickness  of  the  metal  of  plain 


92  PRACTICAL   MARINE   ENGINEERING. 

boiler  tubes  is  usually  from  8  to  12  wire  gauge,  or  from  about 
.17  to  .10  in. 

In  addition  to  the  plain  tubes  fitted  as  before  described, 


Fig.  50.     Prosser  Tube  Expander. 


stay-tubes  are  also  frequently  fitted.     These  are  of  extra  heavy 
metal,  usually  about  %  m-  thickness,  and  specially  fitted  to  the 


Fig.  51.     Beading    Tool. 


tube  sheets  by  screw  joints,  as  shown  in  Fig.  52.     These  tubes 
act  as  stays  between  the  tube  sheets.     Further  reference  to  this 


Fig.  52.    Stay   Tube    with    Ferrule. 

point  will  be  found  under  the  head  of  bracing.  When  stay 
tubes  are  fitted,  it  is  customary  to  bead  over  only  the  back  ends 
of  the  plain  tubes,  as  in  Fig.  48.  Not  infrequently,  however,  no 
stay  tubes  are  fitted,  and  in  such  case  the  plain  tubes  must  be 
beaded  over  on  both  ends  in  order  that  they  may  securely  sup- 


BOILERS.  9.3 

port  the  tube  sheets.  Instead  of  the  ordinary  form  of  boiler 
tube,  the  Serve  tube  of  cross-section,  as  shown  in  Fig.  53,  is 
frequently  fitted.  The  ribs  of  metal  reach  down  into  the  column 
of  hot  gas  moving  through  the  tube  and  furnish  additional  sur- 
face to  absorb  the  heat  and  help  it  through  into  the  water.  The 
surface  on  the  fire  side  is  thus  much  greater  than  the  surface  on 
the  water  side,  while  with  the  plain  tube  it  is  somewhat  less. 


Fig.  55.     New  Admiralty  Ferrule. 


Fig.  53.     Serve  Tube. 

Such  tubes  usually  show  an  increased  evaporation  per  square 
foot  of  surface  measured  on  the  water  side,  of  from  15.  to  20  per 
cent.  Their  increased  weight,  however,  offsets  in  a  measure 
this  increase  of  evaporative  efficiency  per  square  foot  of  surface. 
Reference  may  also  be  made  at  this  point  to  the  use  of  re- 
tarders in  boiler  tubes.  These  are  long  twisted  strips  of  thin 
sheet  steel,  as  shown  in  Fig.  54.  They  are  simply  laid  in  the 
tubes  and  serve  to  give  the  gases  more  or  less  rotary  motion 


Fig.  54.     Retarder. 

and  to  assist  in  throwing  them  outward  against  the  surface  of 
the  tube.  With  forced  draft  and  high  rates  of  combustion  the 
use  of  retarders  has  been  accompanied  with  a  marked  increase 
of  economy.  In  some  cases  both  Serve  tubes  and  retarders 
have  been  fitted,  but  the  special  advantages  of  the  combination 
may  be  called  in  question. 

As  a  measure  of  protection  for  the  back  ends  of  tubes  un- 
der forced  draft,  cast  iron  ferrules  are  sometimes  fitted.      Fig. 


94 


PRACTICAL   MARINE   ENGINEERING. 


52  shows  the  so-called  Admiralty  ferrule  in  place  in  a  stay  tube. 
In  Fig.  55  is  shown  an  improved  type  of  ferrule  which  by  rea- 
son of  the  air  space  is  believed  to  act  still  more  efficiently  to 
protect  the  tube  sheet  than  the  form  shown  in  Fig.  52. 

Bracing. — We  must  now  consider  the  bracing  needed  to 
make  the  boiler  perfectly  secure  and  safe  under  the  pressures 


Fig.  56.    Adamson  Ring. 


Fig.  57.     Bowling  Ring. 


to  which  the  various  parts  will  be  subjected.  The  general  prin- 
ciples to  be  kept  in  mind  are  as  follows :  (a)  Cylindrical  surfaces 
subjected  to  pressure  on  the  concave  side  are  not  helped  by 
bracing.  They  must  be  made  sufficiently  strong  by  giving  to 
the  material  a  suitable  thickness,  (b)  Cylindrical  surfaces  sub- 
jected to  pressure  on  the  convex  side  may  be  stayed  like  a  flat 


Fig.  58.    Main   Head   Brace. 

surface,  or  they  may  be  stiffened  by  ribs  running  around  them 
in  planes  at  right  angles  to  the  axis,  (c)  Flat  surfaces  will  sup- 
port themselves  if  their  area  is  sufficiently  small  in  relation  to 
their  thickness  and  to  the  load  per  square  inch,  and  it  follows 
that  large,  flat  surfaces  must  be  sub-divided  into  parts  of  such 
size  that  they  may  thus  become  self-supporting. 


BOILERS.  95 

As  an  illustration  of  (b),  furnaces  were  formerly  strength- 
ened in  this  way,  and  the  long  favorite  Adamson  ring,  as  shown 
in  Fig.  56,  or  the  Bowling  ring,  as  shown  in  Fig.  57,  may  be 
taken  as  good  illustrations  of  this  mode  of  adding  support  to 
cylindrical  surfaces  loaded  .on  the  convex  side.  The  present 
corrugated  furnace,  especially  the  Purves  type,  as  shown  in  Fig. 
41,  may  be  considered  as  a  further  illustration  of  the  same  prin- 
ciple. In  modern  marine  boilers,  aside  from  the  furnaces,  this 
mode  of  support  is  chiefly  used  to  stiffen  the  bottom  of  single 
combustion  chambers  where  screw  stay  bolts  could  not  be  read- 
ily fitted,  and  also  in  some  cases  the  curved  tops  of  combustion 
chambers.  See  Fig.  45. 

Coming  next  to  flat  surfaces  as  referred  to  under  (c),  the 
necessary  sub-division  is  provided  by  the  fitting  of  braces  con- 
necting the  part  to  be  supported  to  some  point  where  the  sup- 
port can  be  provided,  or  by  connecting  together  two  surfaces 
urged  by  the  steam  pressure  in  opposite  directions,  as  for  ex- 
ample the  two  opposite  heads  of  a  boiler,  as  shown  in  Figs.  9, 
ii.  Occasionally  also  flat  surfaces  are  aided  by  attaching  to 
them  stiffening  ribs  of  angle  or  tee  bar,  as  on  the  front  tube 
sheet,  between  the  nests  of  tubes,  or  between  the  tubes  and  the 
shell. 

Plates  which  are  subjected  to  the  direct  action  of  the  fire, 
as  in  the  furnace  and  combustion  chambers,  are  made  relatively 
thin.  This  is  done  because  a  thin  plate  transmits  heat  better 
than  a  thick  one,  and  is  subjected  to  less  severe  internal  stresses 
due  to  the  difference  in  temperature  of  its  two  faces.  The  thin- 
ner the  plate,  however,  the  less  the  area  which  will  be  self  sup- 
porting. Hence  the  braces  for  thin  flat  plates  are  relatively 
small  and  closely  spaced,  while  those  for  thick  plates  are  larger 
and  spaced  at  greater  intervals. 

The  main  head  braces  are  secured  as  shown  in  Fig.  58.  A 
washer  is  fitted  on  the  outside  to  increase  the  supported  area, 
and  a  nut  is  fitted  both  inside  and  outside  so  that  the  joint  may 
readily  be  made  tight,  and  that  the  brace  may,  if  needed,  act  as 
a  strut  against  pressure  from  without  as  well  as  a  tie  against 
pressure  from  within.  In  some  cases  a  relatively  thin  plate  is 
supported  by  a  brace  connecting  it  to  a  thicker  or  perhaps  to  a 
double  plate,  or  to  a  place  not  requiring  support  itself,  but  which 
furnishes  a  convenient  point  for  carrying  the  load.  In  such 
case  the  attachment  to  the  thin  plate  is  often  made,  as  shown  in 


96 


PRACTICAL   MARINE   ENGINEERING. 


Fig.  59,  in  order  the  better  to  sub-divide  and  distribute  the  sup- 
port. In  double-ended  boilers,  certain  parts  of  the  head,  as 
for  example  those  between  the  furnaces,  are  supported  by 
braces  running  obliquely  back  to  the  shell  and  attached  as 
shown  in  Fig.  60.  It  often  thus  happens  that  braces  must  run 
at  a  slight  obliquity  in  order  to  connect  the  parts  to  be  sup- 
ported with  convenient  points  of  support.  Other  instances  are 


Fig.  59.    Forked  End  Brace. 

often  found  in  the  braces  connecting  parts  of  the  back  tube 
sheet  below  or  between  the  tubes  to  the  boiler  head.  In  all 
such  cases,  wedge-shaped  washers,  as  shown  in  Fig.  61,  must  be 
fitted  under  the  nuts  in  order  to  get  a  good  bearing  between  the 
nut  and  the  shell. 

The  braces  connecting  the  relatively  thin  plates  of  the  com- 
bustion chamber  to  the  back  head  and  shell  of  the  boiler  and  to 


BOILERS. 


97 


each  other,  are  fitted  by  screwing  them  through  into  both  plates, 
as  shown  in  Fig.  62.  The  ends  are  sometimes  riveted  over  and 
sometimes  fitted  with  nuts.  In  some  cases  thev  are  left  thread- 


OO| 


o  oj 


Fig.  60.     Flange  Foot  Brace. 


ed  the  entire  length,  in  others  the  threads  are  raised  on  the  ends, 
as  in  the  main  head  braces.  The  latter  practice  is  much  to  be 
preferred.  These  braces  are  commonly  known  as  "screw 


Fig.  61.    Oblique   Brace. 

stays,"  or  "screw  staybolts."  This  mode  of  fitting  enables  the 
screw  stay  bolt  to  act  both  as  strut  and  as  tie,  or  to  resist  pres- 
sure in  both  directions.  In  some  cases  the  older  form  of 
"socket  bolt,"  as  illustrated  in  Fig.  63  is  still  fitted.  In  such 


PRACTICAL  MARINE   ENGINEERING. 


case  the  head  is  riveted  and  the  part  of  the  bolt  between  the 
plates  is  provided  with  a  hollow  "socket."  This  acts  as  a  strut 
and  as  a  protection  to  the  bolt  proper.  In  modern  approved 
practice  screw  stay  bolts  are  either  hollow  or  are  drilled  in  at 


Fig.  62.    Screw    Stay    Bolt. 

each  end  (see  Fig.  64),  to  a  point  well  beyond  the  inner  face  of 
the  supported  plate.  The  expansion  and  contraction  of  such 
parts  of  the  boiler  often  have  the  effect  of  bending  these  bolts 


Fig.  63.    Socket  Bolt. 

back  and  forth,  and  they  may  thus  in  time  become  broken  off, 
the  break  naturally  occurring  near  the  thicker  of  the  two  sheets 
where  the  bolt  is  held  more  rigidly.  If  this  should  occur,  or 


Fig.  64.    Improved  Screw  Stay. 

if  the  bolt  should  become  badly  corroded  or  pitted,  especially 
near  the  plate,  warning  will  be  given  of  the  fact  by  the  escape 
of  water  or  steam,  and  proper  means  must  be  taken  for  replac- 
ing the  bolt.  In  this  way  timely  warning  may  be  given  of  a 


BOILERS. 


99 


condition  of  affairs,  which  if  allowed  to  go  unnoted,  might  re- 
sult in  a  collapse  of  the  plate,  or  in  a  disastrous  explosion  of 
the  boiler  as  a  whole. 

The  usual  spacing  of  stays,  such  as  that  shown  in  Fig.  58, 


o      o       o       o 

COMBUSTION   CHAMBER 
0000 

O  O  O  O 


Fig.  65.    Girder  Brace  or  Crown  Bar. 


and  supporting  plates  not  directly  exposed  to  the  hot  flames  or 
gases  is  from  14  to  16  inches  between  centers,  while  for  screw 


Fig.  66.     Flanged  Manhole  and  Fitting. 

stays  supporting  plates  more  or  less  directly  exposed  to  the  fire, 
the  spacing  is  usually  between  6  to  8  inches.  See  also  on  this 
point  Sec.  62. 

For  the  support  of  the  top  of  the  combustion  chamber,  gird- 


IOO 


PRACTICAL   MARINE   ENGINEERING. 


ers  or  crown-bars  are  used,  see  Fig.  65.     The  load  is  transferred 
by  means  of  the  bolts  from  the  combustion  chamber  plate  to  the 


Fig.  67.    Reinforce    Plate. 


girder,  while  the  latter  is  supported  by  the  edges  of  the  vertical 
plates  forming  the  front  and  back  of  the  chamber. 

These  girders  are  made  of  two  pieces  of  steel  plate,  usually 
from  y2  to  3.4  in.  thick,  bolted  or  riveted  together  with  distance 


oooooo 


Fig.  68.     Manhole  and  Fitting 
in  Shell  of  Boiler. 


Fig.  69.    Reinforce    Plate. 


pieces  between  so  that  the  bolts  which  take  the  load  from  the 
flat  plate  may  pass  up  between  them  as  shown  in  the  figure. 

The  combustion  chamber  is  sometimes  secured  to  the  back 
head  of  the  boiler,  or  in  double-ended  boilers  the  two  combus- 
tion chambers  are  secured  together  by  plate  braces  fitted  as 
shown  in  Fig.  45.  Such  are  usually  called  gusset  braces. 

In  the  general  internal  arrangement  of  the  tubes,  furnaces 


BOILERS. 


and  combustion  chambers,  care  must  be  taken  to  allow,  as  far 
as  possible,  a  ready  examination  of  the  various  parts.  In  good 
modern  practice  a  space  of  from  10  to  12  inches  is  left  between 
the  nests  of  tubes  and  between  the  tubes  and  shell,  so  as  to  al- 
low the  passage  of  a  man  from  the  steam  space  down  through 
these  spaces  to  the  furnaces. 

Manholes  and  Covers. — For  the  purpose  of  entering,  ex- 
amining and  cleaning  the  interior  of  a  boiler,  man  or  hand  holes 
are  cut  in  the  head  or  shell.  These  are  then  covered  by  man- 
hole covers,  plates  or  doors,  as  they  are  variously  called.  These 


Fig.  70.    Manhole  Plate  and  Fittings. 

are  secured  by  bolts  and  dogs,  as  shown  in  Figs.  66-70.  The 
usual  size  of  a  manhole  is  n  by  15  inches,  which  are  the  dimen- 
sions required  by  the  U.  S.  rules.  It  is  of  oval  or  elliptical 
shape,  so  that  the  cover  with  its  lip  extending  over  the  edge 
may  be  gotten  in  and  out  without  difficulty.  The  joint  is  made 
on  the  inside  in  order  that  the  pressure  may  tend  to  keep  the 
joint  tight.  A  hand-hole  is  entirely  similar  in  shape  and  fitting, 
and  is  simply  smaller  in  size.  In  order  to  provide  local  strength 
and  stiffness  and  to  help  support  the  load  which  comes  on  the 
feet  of  the  dog,  and  also  when  the  hole  is  cut  in  the  shell 


•ic^^U       PRACTICAL   MARINE   ENGINEERING. 

to  restore  in  some  measure  the  metal  taken  out,  a 
reinforce  ring  of  metal  is  fitted  about  the  hole.  Such 
a  ring  of  cast  steel  for  a  hole  in  the  shell  is  shown 
in  Fig.  68.  The  inner  face  is  planed,  so  that  the  joint  with 
the  cover  is  readily  made.  In  order  that  the  removal  of  the 
metal  may  affect  as  little  as  possible  the  strength  of  the  shell, 
the  longer  axis  of  the  hole  should  run  around  the  boiler  rather 
than  lengthwise.  For  holes  in  the  head  of  a  boiler  the  metal  is 
often  flanged  inward,  as  shown  in  Fig.  66,  the  joint  being  made 
against  the  dressed  edge  of  the  ring.  Where  a  manhole  or 
handhole  comes  close  to  through  braces,  as,  for  example,  near 


Fig.  71.     Furnace  Front. 

the  furnaces,  the  reinforce  plate  may  be  formed,  as  shown  in 
Figs.  67  and  69.  At  the  angles  or  corners  the  plate  is  of  suffi- 
cient width  to  let  the  threaded  end  of  the  brace  come  through, 
and  the  outside  nut  is  then  jammed  down  on  the  ring  as  shown. 
For  heavy  pressure  the  fitting  illustrated  in  Fig.  70  may  be  rec- 
ommended. The  reinforce  ring  is  of  flanged  steel,  and  the 
cover  of  steel  plate  also,  somewhat  thicker  than  the  metal  of  the 
shell.  An  angle  iron,  as  shown,  is  riveted  to  the  cover,  making 
a  neat  fit  within  the  reinforce  ring,  and  keeping  the  plate  ac- 
curately to  its  seat. 

Furnace  Fronts  and  Doors. — The  furnace  front  is  a  fitting  at- 
tached to  the  mouth  of  the  furnace,  and  carrying  the  furnace 


BOILERS. 


103 


door.  In  Figs.  71,  72  a  common  form  of  arrangement  is  shown. 
The  front  consists  of  a  steel  plate  forming  the  outer  part, 
and  made  with  lugs  or  a  flange  for  attachment  to  the  furnace. 
The  opening  for  the  door  is  formed,  as  shown,  within  this  front 
or  door  frame  as  it  is  sometimes  called.  Attached  to  this  frame 
and  with  a  space  between  is  a  second  plate  of  cast  iron 
forming  the  inner  wall.  This  is  pierced  with  a  large  number  of 
small  holes,  while  the  frame  is  provided  with  a  smaller  number 
of  larger  holes.  These  are  provided  for  the  purpose  of  admit- 
ting air  to  the  furnace  above  the  grate.  The  inner  plate  is  sub- 
ject to  the  direct  action  of  the  fire,  and  although  cooled  some- 
what by  the  air  passing  through,  it  is  liable  to  burn  out  from 


/vfv.f.n  i\ — , i 

/vTi 


Fig.  12.     Detail    of    Furnace    Front. 

time  to  time.  It  is  for  this  reason  that  it  is  made  as  a  separate 
piece,  and  so  is  readily  replaced  as  occasion  requires.  The  door 
is  formed  in  much  the  same  way  as  the  frame,  and  is  provided 
with  holes  in  a  similar  fashion  and  for  the  same  purpose.  Often 
a  small  covered  peep-hole  is  provided  for  examining  the  fire 
without  opening  the  door.  In  some  cases  also  a  small  opening 
is  made  through  which  a  slice  bar  may  be  introduced  for  stirring 
or  breaking  up  the  fire  without  opening  the  door.  A  form  of 
slide  or  gridiron  is  also  sometimes  fitted  so  as  to  control  the 
amount  of  air  entering  above  the  grates.  In  some  cases  the 
doors  and  frames  are  made  entirely  of  flanged  steel  plates  in- 
stead of  cast  iron,  while  much  variety  exists  in  the  arrangement 


104 


PRACTICAL   MARINE   ENGINEERING. 


of  the  holes  for  the  introduction  of  the  air.  Certain  special 
fittings  necessary  to  adapt  the  'furnace  fronts  and  doors  to  the 
application  of  forced  draft  will  be  referred  to  at  a  later  point. 

The  ash-pit  door  usually  consists  simply  of  a  plate  of  thin 
sheet  steel  provided  with  the  necessary  lugs  and  handles,  and 
covering  the  front  opening  in  the  furnace  below  the  grate  bars. 
It  is  used  chiefly  as  a  damper  in  connection  with  closed  stoke- 
hold forced  draft. 

Grate  and  Bridge  Walls. — The  general  arrangement  of  the 
inside  of  the  furnace  is  illustrated  in  Fig.  73.  The  grate 
extends  from  the  front  of  the  furnace  to  the  bridge  wall  as 
shown.  The  bottom  of  the  door  frame  extends  back  a  little 


Fig.  73.    Section  of  Furnace  and   Grate. 

way  and  drops  down,  forming  a  kind  of  shelf  for  the  support 
of  the  front  ends  of  the  grate  bars.  In  some  cases  this  exten- 
sion of  the  door  frame  extends  back  some  distance,  forming  the 
so-called  dead  plate,  upon  which  bituminous  coal  may  be  piled 
when  first  fired,  so  as  to  provide  for  the  gradual  distillation  and 
combustion  of  its  gases. 

The  great  bars  may  be  made  in  a  large  variety  of  forms. 
In  Fig.  74  is  shown  the  standard  type  of  cast  iron  bar.  There 
are  usually  two  lengths  of  bar  in  the  length  of  the  furnace,  sup- 
ported by  the  door  frame  in  front  and  bridge  wall  at  the  rear, 
and  by  bearing  bars  in  the  middle.  These  latter  in  turn  are  sup- 


BOILERS.  105 

ported  at  their  ends  by  attachment  to  the  furnace.  The  bars 
are  usually  cast  double,  as  shown,  while  for  convenience  in  fit- 
ting grates  of  varying  widths,  a  small  number  of  single  bars  are 
usually  provided.  The  width  of  air  space  between  the  bars  is 
usually  made  about  equal  to  the  width  of  the  bar,  or  about  one- 
half  of  the  entire  grate  area,  although  this  proportion  should 
vary  somewhat  according  to  the  fuel  in  use.  The  surface 
of  the  grate  usually  slopes  slightly  from  front  to  rear, 
from  i  in  24  to  i  in  12,  covering  the  usual  range  of  angle.  Cast 
iron  grate  bars  often  have  a  shallow  groove  running  along  the 
top.  This  fills  with  ashes  and  tends  to  prevent  the  clinkers  ad- 
hering to  the  grate. 

In  addition  to  the  type  of  bar  shown  in  Fig.  74,  square 
wrought  iron  bars  running  the  whole  length  of  the  furnace  are 
sometimes  used,  and  there  is  a  large  variety  of  patent  and  spe- 
cial kinds  of  shaking  grate.  The  purpose  in  grates  of  this  char- 


Fig.  74.    Grate   Bar. 

acter  is  to  provide  means  for  breaking  up  and  working  the  fire 
without  the  need  of  opening  the  door.  Many  of  them  accom- 
plish this  end  to  a  considerable  extent,  but  the  greater  simplicity 
and  cheapness  of  the  plain  cast  iron  grate,  as  in  Fig.  74,  insures 
for  the  latter  a  wide  use,  and  it  is  still  the  favorite  in  ordinary 
practice. 

Turning  now  to  the  bridge  wall,  a  common  arrangement  is 
shown  in  Fig.  73.  A  casting  extends  across  the  back  of  the 
furnace  and  is  supported  by  attachment  at  the  sides.  This  sup- 
ports the  back  ends  of  the  grate  bars,  as  already  referred  to, 
and  also  a  wall  of  fire  brick  which  forms  the  back  limit  of  the 
grate,  and  over  which  the  products  of  combustion  pass  on  their 
way  to  the  combustion  chamber. 

Instead  of  fire-brick,  the  use  of  cast  iron  for  bridges  is  be- 
coming frequent  in  modern  advanced  practice.  Such  bridges 
are  of  ribbed  or  channeled  form,  and  in  use  they  become  suffi- 


io6 


PRACTICAL   MARINE   ENGINEERING. 


ciently  covered  with  ashes  to  form  a  protection  against  the  heat 
of  the  fire. 

Front  Connections  and  Funnel. — After  leaving  the  tubes  at 
the  front  end  the  gases  and  smoke  must  be  guided  to  the  base 
of  the  funnel.  This  is  done  by  the  front  connections  or  smoke 
boxes  and  uptakes,  as  shown  in  the  diagrams.  Fig.  75  shows 
the  connection  made  between  two  single-ended  boilers  and  one 
funnel,  used  in  common  by  both.  The  boilers  are  placed  front 
to  front  in  an  athwartship  fire  room.  Fig.  76  shows  the  connec- 
tions between  one  double-ended  boiler  and  the  smoke  pipe. 


Fig.  75.     Front    Connections,    Uptakes    and    Funnel    Base. 

These  connections  are  formed  of  sheet  metal  riveted  up  in  two 
or  more  thicknesses  with  an  air  space  or  non-conducting  ma- 
terial between.  The  term  front  connection  refers  more  especially 
to  that  part  of  the  passage  directly  in  front  of  the  tubes.  This 
is  provided  with  doors  swinging  upward  to  allow  examination, 
cleaning  and  repair  of  the  tubes.  A  swinging  damper  is  often 
placed  in  the  uptakes  for  controlling  the  draft  as  may  be  de- 
sired, especially  where  two  or  more  boilers  are  connected  to  one 
stack.  The  funnel  or  stack  is  also  made  of  sheet  metal  riveted 
up,  and  in  good  practice  in  two  thicknesses  with  a  considerable 


BOILERS. 


107 


air  space  between.  This  tends  to  prevent  loss  of  heat  by  radia- 
tion, and  thus  the  temperature  of  the  gases  is  kept  as  high  as 
possible  while  in  the  funnel,  as  is  necessary  for  good  draft.  It 
may  be  remembered  that  for  boiler  economy  the  temperature  of 
the  waste  gases  at  the  front  connection  should  be  as  low  as 
possible,  while  for  the  sake  of  the  draft  all  further  loss  of  heat 
while  in  the  funnel  should  be  prevented.  Around  the  base  of 
the  funnel  is  fitted  an  additional  air  screen  or  passage, 
known  as  the  air  casing.  See  Fig.  77.  This  serves  to  ventilate 


DO 


JBLE   ENI 
BOILER 


fl 


ED 


n    n 


Fig.  76.     Front   Connections  and   Uptakes. 

the  fire-rooms  and  to  protect  the  neighboring  parts  of  the  ship 
from  the  heat  radiated  by  the  funnel.  The  air  casing  is  pro- 
tected from  the  weather  by  a  sloping  ring  of  metal  attached  to 
the  funnel,  as  shown  in  the  figure,  and  known  as  the  umbrella. 

The  weight  of  the  funnel  is  usually  carried  by  straps  or  lugs 
attached  to  the  structure  of  the  ship,  and  it  is  furthermore  stayed 
by  guys  on  deck  in  order  to  provide  the  necessary  steadiness 
and  support  in  a  sea-way.  In  small  craft,  however,  the  weight 
of  the  funnel  is  often  taken  simply  by  the  uptakes  and  boilers. 


io8 


PRACTICAL   MARINE   ENGINEERING. 


The  funnel  is  often  provided  with  a  cover,  which  may  be 
placed  over  the  top  when  the  ship  is  laid  up,  or  when  for  other 
reason  the  funnel  is  not  in  use.  The  cover  is  usually  kept  a  lit- 
tle distance  above  the  top  so  as  to  allow  the  escape  of  smoke 
from  small  fires  used  for  warming  and  airing  the  boilers.  A 
ladderway  should  also  be  provided  on  the  funnel  to  assist  in  ex- 
amination, adjustment  of  guys,  fitting  of  cover,  etc.  In  small 


OUTER    STACK 


DECK  DECK 


Fig.  77.    Funnel. 

craft  a  damper  is  often  fitted  in  the  funnel  near  the  base,  to  as- 
sist in  controlling  the  draft. 

[4]  Construction  of  Water- Tube  Boilers. 

Only  a  few  points  will  require  special  notice  under  this 
heading.  We  have  already  seen  that  many  types  of  water-tube 
boiler  consist  of  one  or  more  cylindrical  drums  above  and  one 
or  more  below,  joined  by  a  series  of  tubes.  See  Figs.  15-26. 
These  drums,  which  are  rarely  more  than  18  to  24  in.  diameter, 


BOILERS.  iog> 

are  made  from  steel  plates  usually  by  flanging  and  riveting  in  the 
usual  manner.  The  heads  alone  of  such  drums  require  con- 
sideration as  regards  bracing.  If  of  sufficient  size  to  require 
it  they  may  be  braced  by  through  bolts  as  with  boiler  heads. 
In  most  cases,  however,  the  heads  are  bumped  or  made  of 
dished  form,  either  concave  or  convex  on  the  outside.  The  lat- 
ter is  preferable,  as  the  pressure  is  then  carried  on  the  concave 
side,  and  according  to  the  United  States  law  such  heads  are 
allowed  without  bracing  a  pressure  the  same  as  that  for  a 
cylindrical  shell  of  a  diameter  equal  to  the  radius  of  the  sphere 
of  which  the  head  forms  a  part. 

It  is  much  preferable  to  form  the  heads  in  this  way,  avoid- 
ing the  need  of  bracing,  and  thus  leaving  the  interior  of  the 
drum  free  for  examination,  at  least  so  far  as  bracing  is  con- 
cerned. To  allow  access  to  the  interior,  manholes  or  hand- 
holes  with  appropriate  cover  plates  are  fitted  to  the  heads.  In- 
stead of  forming  these  drums  with  riveted  joints,  drums  with 
welded  joints  have  recently  come  somewhat  into  use,  especially 
in  naval  practice. 

With  boilers  having  headers  formed  by  the  space  between 
two  parallel  sheets,  the  necessary  arrangements  are  quite  differ- 
ent. These  sheets  require  special  support,  and  this  is  usually 
provided  by  screw  stay-bolts  or  other  equivalent  stays  worked 
between  the  two  sheets  attached  to  the  tube  sheet  between  the 
tubes  as  convenient,  and  securely  tying  the  two  sheets  together. 
In  some  cases  the  outer  sheets  are  supported  by  rod  stays  pass- 
ing from  head  to  head  through  the  tubes.  In  such  case  the 
tube  sheets  are  left  to  be  supported  by  the  tubes  which  are  thus 
thrown  into  compression,  and  the  tubes  must,  therefore,  be 
carefully  expanded,  especially  on  the  inner  side  of  the  sheet,  in 
order  to  give  sufficient  hold  to  support  the  sheets  in  this  direc- 
tion. 

In  Sec.  14  [6]  in  speaking  of  the  operation  of  water-tube 
boilers,  reference  was  made  to  a  separation  in  the  upper  drum 
of  the  water  and  the  steam  as  they  are  delivered  from  the  upper 
ends  of  the  tubes.  This  is  usually  effected  by  some  form  of 
baffle  plate,  as  illustrated  in  Fig.  17.  A  plate  pierced  with 
small  holes  is  placed  just  in  front  of  .the  tube  openings,  and 
against  this  the  escaping  jets  of  water  and  steam  are  directed. 
The  water  is  supposed  to  collect  on  the  plate  and  to  run  down 
to  the  lower  edge,  or  to  the  water  in  the  lower  part  of  the  drum, 


i io  PRACTICAL   MARINE   ENGINEERING. 

while  the  steam  passes  through  the  holes  and  enters  the  steam 
pipe  beyond.  In  the  Bellville  boiler,  as  in  Fig.  26,  there  is  a 
series  of  baffle  plates  forming  a  more  or  less  tortuous  passage 
through  which  the  steam  must  pass  on  its  way  to  the  outlet, 
while  at  the  last  there  is  a  plate  with  holes  which  exercise  a 
straining  action  in  the  manner  described  just  above.  Special 
separators,  as  described  in  Sec.  35,  are  sometimes  fitted  in  ad- 
dition to  these  internal  separating  devices. 

The  tubes  of  water-tube  boilers  are  of  wrought  iron  or 
steel,  and  welded  or  solid  drawn.  For  the  bent-tube  boilers 
solid  drawn  steel  tubes  are  to  be  preferred.  For  straight  tube 
boilers  welded  iron  tubes  are  still  in  common  use.  The  tubes 
are  secured  to  the  tube  sheets  either  by  expanding  or  by  special 
fittings  with  screwed  joints.  In  general  there  is  a  force  tending 
to  draw  the  tubes  out  of  the  tube  sheet  or  junction  box  or 
other  form  of  header,  equal  for  each  tube  to  its  cross-sectional 
area  multiplied  by  the  steam  pressure.  This  force  must  be  re- 
sisted by  the  tube  fastening,  and  while  it  is  not  usually  serious 
in  amount,  its  existence  should  not  be  forgotten,  and  the  need 
of  care  in  the  fastening  is  shown. 

The  furnaces  of  water-tube  boilers  are  formed  of  grate-bars 
with  a  space  below  for  ash-pit,  all  inclosed  in  the  same  general 
casing  which  surrounds  the  boiler  as  a  whole,  and  as  shown  in 
the  various  figures  referred  to  in  the  foregoing. 

Often  a  considerable  amount  of  fire-brick  is  used  as  a  lining 
to  the  furnace,  and  for  protection  to  the  lower  ends  of  the  tubes. 

Due  to  the  great  variety  of  forms  of  water-tube  boilers,  the 
details  of  construction  often  present  the  widest  variation,  and 
they  cannot  be  so  readily  reduced  to  standard  forms  as  in  boil- 
ers of  the  fire-tube  type. 

[5]  Common  Sizes  and  Dimensions  of  Scotch  Boilers. 

The  furnace  diameter  for  Scotch  boilers  is  usually  found  be- 
tween 42  and  48  inches.  The  upper  limit  comes  about  in  the 
following  manner.  Taking  into  account  the  extreme  ranges  of 
temperature  to  which  this  part  of  the  boiler  is  subjected,  and 
based  on  general  experience,  it  is  usually  considered  that  from 
Y-2  to  y%  inch  is  about  as  far  as  it  is  desirable  to  carry  at  present 
the  thickness  of  the  metal  for  the  furnace. 

Again  the  strength  of  the  furnace  increases  with  the  thick- 
ness and  decreases  with  the  diameter.  Hence  for  a  given  pres- 
sure and  limit  on  the  thickness,  the  diameter  will  be  limited  as 


BOILERS.  in 

well.  With  modern  pressures  and  a  general  limit  on  the  thick- 
ness as  above,  the  limit  on  the  diameter,  therefore,  results. 
Rarely  furnaces  are  met  with  up  to  54  in.,  but  only  with  the 
more  moderate  steam  pressures.  The  lower  limit  for  furnace 
diameter  is  given  by  a  consideration  of  the  necessary  space  be- 
tween the  fire  and  the  furnace  crown.  If  this  space  or  height 
is  not  sufficient  the  fires  cannot  be  properly  worked  and  the 
combustion  will  be  incomplete,  due  to  insufficient  space  for  the 
admixture  of  air  with  the  gases  given  off  from  the  coal. 

In  fact  for  efficiency  of  combustion  we  should  probably  pre- 
fer the  diameter  of  the  furnace  larger  than  we  are  actually  able 
to  fit.  As  a  lower  limit,  however,  it  may  be  considered  inad- 
visable to  fit  furnaces  much  smaller  than  42  inches,  though  they 
are  sometimes  found  down  to  36  inches. 

The  length  of  fire  grate  is  usually  found  between  5  and  6 
feet,  though  occasionally  it  extends  to  6  ft.  6  in.,  or  may  be 
found  as  short  as  4  ft.  6  in.  The  chief  limitation  here  comes 
from  the  limit  in  the  capacity  of  the  average  fireman  to  efficient- 
ly work  his  fire  beyond  a  certain  length.  For  average  practice 
5  ft.  6  in.  may  be  considered  a  good  length,  while  it  is  doubtful 
if  grate  area  added  beyond  this  length  will  be  of  any  great  value 
for  steam  production.  It  is  more  than  likely  to  become  partially 
choked  with  ashes  and  clinker,  while  a  shorter  grate  of  5  ft.  or 
5  ft.  6  in.  length  may  be  kept  bright  and  efficient  over  its  entire 
surface. 

The  length  of  the  furnace  itself  being  equal  to  the  tubes  will 
be  somewhat  longer  than  the  grate.  The  difference  is  usually 
from  12  to  24  or  even  30  inches. 

This  gyves  for  the  usual  length  of  furnace  and  of  tubes  from 
7  to  9  feet. 

The  usual  depth  of  the  combustion  chamber  is  from  24  to 
30  inches.  This  will  usually  give  a  suitable  volume,  and  will 
also  provide  a  sufficient  space  within  which  a  man  may  swing 
a  hammer  or  make  use  of  such  other  tools  as  may  be  necessary 
in  caring  for  the  back  ends  of  the  tubes. 

The  usual  thickness  of  the  water  leg  or  space  between  the 
back  of  the  combustion  chamber  and  the  back  head  of  the  boiler 
is  from  6  to  9  inches. 

It  will  thus  be  seen  that  the  usual  length  of  a  Scotch  single- 
end  boiler  will  be  found  between  10  and  12  feet ;  10  ft.  6  in.  and 
IT  ft.  are  quite  common  values. 


ii2  PRACTICAL   MARINE   ENGINEERING. 

Comparing  the  construction  of  a  single  and  double  end 
boiler  it  is  clear  that  the  length  of  the  latter  will  be  slightly  less 
than  twice  the  length  of  a  single  end.  This  gives  for  the  usual 
length  of  a  double-end  boiler  from  18  to  21  feet. 

The  diameter  of  the  boiler  will  depend  largely  on  the  num- 
ber of  furnaces  to  be  fitted,  and,  of  course,  on  the  steam  pres- 
sure and  on  any  limitations  in  the  thickness  of  the  plates  em- 
ployed. Modern  four-furnace  boilers  are  usually  found  between 
15  and  17  feet  in  diameter.  For  three-furnace  boilers  the  di- 
ameters will  similarly  range  from  13  to  14  feet,  while  for  two- 
furnace  boilers  the  diameter  may  vary  from  10  feet  or  less  to 
ii  or  12  feet. 

The  usual  diameter  for  tubes  is  from  2%  to  3  inches.  The 
smaller  sizes  are  used  with  forced  draft  and  the  higher  rates  of 
combustion.  For  natural  draft  2^4  and  3  inches  are  common 
sizes. 

The  thickness  of  boiler  tubes  is  usually  specified  by  sheet 
metal  gauge  number.  Plain  tubes  are  usually  No.  8,  10  or  12, 
corresponding  to  .17  to  .10  inch.  Stay  tubes  are  usually  about 
No.  3  or  J4  mcn  m  thickness. 

[6]  Common  Proportions  for  Scotch  Boilers. 

Grate  Surface  (G.  S.)     10  to  15  I.  H.  P.  per  sq.  ft.  G.  S. 

Heating  Surface  (H.  S.)  2  to  5  square  feet  per  I.  H.  P.  or 
25  to  40  square  feet  per  sq.  ft.  G.  S. 

Coal  Burned.  15  to  30  Ibs.  per  sq.  ft.  G.  S.  per  hour,  or 
J/2  to  i  lb.  per  sq.  ft.  H.  S.  per  hour. 

Water  Evaporated.  6  to  10  Ibs.  per  lb.  of  coal,  or  4  to  10 
Ibs.  per  sq.  ft.  H.  S.  per  hour. 

Section  of  Passage  Over  Bridge  Wall.     1-6  to  1-8  G.  S. 

Sectional  Area  of  Tubes.     1-5  to  1-7  G.  S. 

Sectional  Area  of  Funnel.    1-6  to  1-8  G.  S. 

Volume  of  Combustion  Chamber.  3  to  4  cu.  ft.  per  sq.  ft. 
of  G.  S. 

Steam  Volume.     .3  to  .4  cu.  ft.  per  I.  H.  P. 

[7]  Weights  of  Boilers. 

A  modern  four-furnace  single-end  Scotch  boiler  will  weigh 
in  the  neighborhood  of  40  tons,  or  upward,  while  the  water  will 
weigh  not  far  from  20  tons,  making  60  tons  or  more  for 
the  boiler  as  a  whole.  A  four-furnace  double-end  boiler  will 
similarly  weigh  not  far  from  70  tons,  while  the  water  will  weigh 


BOILERS.  113 

not  far  from  40  tons,  making  no  tons  more  or  less  for  the  boiler 
as  a  whole.  For  a  modern  three-furnace  single-end  boiler  the 
weights  would  be  similarly  about  25,  15  and  40  tons,  respec- 
tively, for  boiler,  water  and  total,  while  for  a  three-furnace 
double-end  boiler  they  would  be  about  45,  25,  and  70  tons,  re- 
spectively, for  boiler,  water  and  total.  Wide  variations,  of 
course,  are  found  in  the  weights  of  boilers,  and  the  above  figures 
are  only  given  to  show  the  general  nature  of  the  weights  in- 
volved. The  weight  of  boilers  with  and  without  water,  per 
square  foot  of  heating  surface,  has  already  been  noted  in  Sec. 
14.  From  these  various  figures  and  proportions  it  results  that 
Scotch  boilers  may  be  expected  to  develop  from  20  to  30  I.  H. 
P.  per  ton  according  to  conditions,  while  for  water-tube  boilers 
the  figures  will"  run  from  30  or  40  for  the  heavier  types  to  6c 
or  70  and  even  more  for  the  lighter  types,  and  with  extreme 
rates  of  forced  draft. 

[8]  Western  River  Boat  or  Flue  Boilers. 

As  noted  in  Sec.  14  these  boilers  are  in  common  use  on  the 
western  rivers  of  the  United  States.  A  few  additional  points 
may  here  be  given  regarding  their  construction  and  installa- 
tion. 

The  length  of  such  boilers  varies  from  20  to  30  feet,  with 
a  diameter  of  about  4  feet  and  with  from  4  to  6  flues  10  to  14 
inches  in  diameter.  The  shells  are  made  up  of  several  courses 
as  shown  in  Fig.  14,  the  circumferential  seams  being  single  riv- 
eted and  the  longitudinal  seams  double  riveted.  The  flues  are 
usually  made  also  in  lengths,  lap  welded  and  telescoped  to- 
gether. 

Such  a  boiler,  for  example,  of  26  feet  length  and  47  inches 
diameter  with  six  10  inch  flues  has  about  580  sq.  ft.  heating 
surface  and  will  provide  steam  for  about  275  I.  H.  P.  in  engines 
of  the  type  commonly  used  and  described  in  Sec.  24. 

When  such  boilers  are  arranged  in  battery  they  are  placed 
side  by  side  and  are  usually  provided  w^ith  a  single  setting,  thus 
giving  a  common  furnace  for  the  entire  battery.  The  length 
of  grate  bar  is  short,  being  usually  about  4  ft.  6  in.  The  boilers 
are  furthermore  usually  connected  by  a  steam  drum  on  top  and 
by  one  or  more  mud  drums  at  the  bottom.  The  steam  drum 
for  the  size  of  boiler  referred  to  above  may  be  from  18  to  24 
inches  in  diameter,  connected  by  legs  12  to  16  inches  in  diameter 


ii4  PRACTICAL  MARINE   ENGINEERING. 

and  spacing  the  boilers  so  as  to  give  flame  room  of  9  to  12 
inches  between  the  shells. 

In  order  to  make  the  setting  of  such  boilers  as  light  as  pos- 
sible the  brick  work  may  be  kept  down  to  a  single  thickness  of 
fire  brick  supported  by  a  sheet  iron  casing.  The  ash  pan  is 
preferably  of  steel  plates  lined  with  fire  brick  laid  in  cement. 
An  interesting  feature  of  the  ash  pan  is  the  ash  well  which  is 
frequently  fitted.  This  consists  of  a  10  or  12  inch  cylindrical 
passage  leading  from  the  surface  of  the  ash  pan  down  through 
the  bottom-  of  the  boat,  and  through  which  the  ashes  are  dis- 
charged overboard  without  further  handling.  The  boiler  fronts 
are  of  cast  iron  with  suitable  fire-door  and  ash-pit  openings. 
The  uptakes,  and  funnels,  or  chimneys  as  they  are  more  com- 
monly called,  are  made  of  heavy  sheet  iron  and  are  supported 
by  bracing  carried  down  to  the  main  deck  beams  which  carry 
the  boilers  themselves. 

As  noted  below  the  engines  work  non-condensing,  and  the 
exhaust,  as  a  rule,  is  led  first  through  the  feed  heaters  to  the 
''Doctor"  as  described  in  Sec.  24,  and  then  to  the  base  of  the 
chimneys  for  forming  a  blast  and  forcing  the  combustion. 
Connections  may  also  be  provided  for  carrying  the  exhaust  to 
an  exhaust  pipe  leading  to  the  air,  and  also  in  part  to  the  stern 
wheel  if  desired,  in  order  to  prevent  the  formation  of  ice  in  cold 
weather. 

Lever  safety  valves,  as  illustrated  in  Fig.  78,  are  usually 
employed  on  these  boilers,  while  gauge  cocks,  fusible  plugs, 
steam  gauges,  and  blow-off  cocks  are  provided  in  accordance 
with  usual  practice. 

The  steam  piping  is  usually  of  lap-welded  wrought  iron  with 
flanged  joints.  One  of  the  chief  features  of  western  river  prac- 
tice is  the  flexibility  of  the  boat  under  different  conditions  of 
lading,  and  the  necessity  for  allowing  for  such  flexibility  in  the 
connections  between  the  boilers  and  engines,  and  between  the 
engines  and  wheel.  Between  the  boilers  and  engines  this  is 
usually  provided  by  the  introduction  of  long  bends  or  special 
connections  intended  to  allow  for  changes  due  to  expansion, 
contraction,  twisting,  etc. 

In  addition  to  the  flue  boiler,  as  illustrated  above,  the  di- 
rect fire  tubular  or  locomotive  type  of  boiler,  as  illustrated  in 
Fig.  12,  is  sometimes  used  on  the  western  rivers,  each  boiler  be- 
ing thus  self-contained,  and  the  brick-work  setting  of  the  flue 


BOILERS.  115 

boilers  being  dispensed  with.  The  flue  boiler,  however,  is  the 
more  used  and  must  be  considered  as  the  typical  boiler  in  this 
field  of  practice. 

Sec.  17.    BOILER  MOUNTINGS  AND  FIRE  ROOM 

FITTINGS. 
[i]  Safety  Valves. 

The  purpose  of  the  safety  valve  is  to  provide  for  the  escape 
of  the  steam  in  case  the  pressure  should  tend  to  rise  above  the 
safe  working  limit  for  which  the  valve  is  set.  There  are  two 
kinds  of  safety  valves,  known  as  lever  and  spring  valves,  accord- 
ing as  the  valve  is  kept  down  on  its  seat  by  a  weight  on  a  lever 
or  by  a  powerful  spring  under  compression.  Fig.  78  shows  the 
construction  of  the  standard  U.  S.  lever  valve. 

The  valve  itself  has  a  plain  conical  face,  and  fits  to  a  corre- 
sponding seat  as  shown.  In  its  motion  up  and  down  it  is  guided 
by  the  double  stem,  so  that  it  can  by  no  means  become  jammed 


Fig.  78.    Standard  Lever  Safety  Valve. 

in  the  chamber.  The  pressure  of  the  steam  comes  on  the  bot- 
tom of  the  valve,  and  as  it  reaches  or  passes  the  limit  for  which 
the  adjustment  is  made  the  valve  lifts  and  the  steam  escapes 
about  the  edge,  and  thence  is  led  by  the  escape  pipe  to  the  deck. 
The  actual  lift  of  a  safety  valve  is  very  small,  l/%  in.  being  usually 
a  large  lift.  The  opening  for  the  escape  of  the  steam  depends, 
therefore,  on  the  circumference  of  the  valve  and  on  the  lift, 
rather  than  on  the  area  and  lift.  Safety  valves  are,  however, 
usually  designated  and  determined  according  to  their  area.  The 
weight  acts  by  means  of  the  lever,  as  shown,  and  may  be  ad- 
justed so  as  to  allow  the  valve  to  open  at  the  pressure  desired. 
On  this  point  consult  further  Sec.  61. 

In  modern  practice  the  lever  valve  is  infrequently  used,  ex- 
cept in  vessels  engaged  in  smooth  water  (river)  service,  the 
spring  valve  being  fitted  almost  universally.  In  this  form  of 


n6 


PRACTICAL   MARINE   ENGINEERING. 


valve,  which  is  shown  in  Fig.  79,  the  chief  point  of  difference  is 
in  the  substitution  of  the  spring  for  the  weight  and  lever.  The 
tension  of  the  spring  is  adjusted  by  a  screw  at  the  top,  so  that 
the  valve  will  not  open  until  the  limiting  pressure  is  reached  or 
exceeded.  It  is  readily  seen  that  as  soon  as  the  valve  rises  the 
spring  is  compressed  and  the  tension  is  increased.  It  is  also 
found  that  with  the  plain  form  of  valve,  as  shown  in  Fig.  78,  the 


m 


Fig.  79.    Double  Spring  Safety  Valve. 

pressure  on  the  face  decreases  the  instant  the  valve  lifts.  Due 
to  these  facts  it  follows  that  such  a  valve,  especially  when  con- 
trolled by  a  spring,  is  apt  to  seat  itself  the  instant  after  rising, 
lifting  again  the  next  instant  in  answer  to  the  restored  value  of 
the  pressure.  This  irregular  action  will  lead  to  a  rapid  opening 
and  closing  of  the  valve,  producing  a  chattering  noise  very  un- 
desirable in  passenger  boats,  and  interfering  with  the  continuous 
and  regular  escape  of  the  steam.  To  avoid  this  a  lip  of  one 


BOILERS. 


117 


form  or  another,  as  shown  in  Figs.  79,  80  and  81,  is  fitted  to  the 
valve  at  or  beyond  the  edge,  so  that  it  may  catch  the  escaping 
jet  of  steam,  and  thus  increase  the  effective  area  of  the  valve 
after  it  has  lifted  from  the  seat.  In  such  case  the  valve  is  forced 
farther  from  the  seat,  and  while  it  still  vibrates,  it  remains  defi- 
nitely open  until  the  pressure  has  fallen  some  4  or  5  Ib.  below 
that  for  which  it  opens.  The  valve  then  touches  the  seat  in  one 
of  its  vibrations  downward,  and  remains  closed  until  the  pres- 


Fig.  80.     Enlarged  Section  of  Lip. 


Fig.  81.    Safety   Valve  and   Muffler. 


sure  again  rises  to  the  point  for  which  it  is  set.  The  safety 
valve  s'hould  always  be  fitted  with  a  hand  lifting  gear,  so  that  it 
may  be  opened  by  hand  when  desired,  and  the  spring  adjustment 
should  be  protected  by  lock  and  key,  so  that  it  cannot  be 
changed  by  unauthorized  persons. 

For  large  boilers,  instead  of  one  large  valve,  safety  valves 
are  often  fitted  in  groups  of  two  or  three.  This  reduces  to  the 
smallest  possible  limit  the  danger  from  sticking  or  other  de- 
rangement of  the  valve.  The  safety  valve  or  valves  should  al- 
ways be  attached  to  a  fitting  leading  direct  to  the  boiler,  and 


ii8  PRACTICAL   MARINE   ENGINEERING. 

with  no  possibility  of  closing  it  off  by  a  stop  valve.  If  both 
stop  and  safety  valves  are  attached  to  the  same  fitting  the'latter 
must  always  be  placed  inside  or  nearer  the  boiler  than  the 
former. 

[2]  Muffler. 

This  fitting,  though  not  in  the  fire-room,  may  be  properly 
referred  to  at  this  point.  It  consists  of  a  metal  chamber  filled 
with  bits  of  metal  or  stone,  marbles,  wire-gauze,  small  spiral 
springs,  or  with  thin  plates  in  layers  pierced  full  of  holes  and  ar- 
ranged in  staggered  fashion  so  as  to  provide  a  series  of  zig-zag 
passages  for  the  steam.  The  steam  from  the  safety  valves  and 
escape  pipe  makes  its  way  to  the  air  through  this  chamber,  the 
purpose  of  the  filling  being  to  muffle  or  deaden  the  noise,  which 
might  otherwise  seriously  interfere  with  the  giving  of  orders  on 
deck.  Fig.  81  shows  a  combined  safety  valve  and  muffler,  the 
latter  with  plates  as  above  described.  Such  an  arrangement 
would  be  applicable  for  small  or  open  craft  having  but  one 
boiler,  such  as  launches,  small  yachts,  etc. 

[3]  Stop  Valve. 

Each  boiler  is  connected  through  a  separate  boiler  steam 
pipe  to  the  main  pipe.  The  entrance  of  steam  to  this  pipe  is 
controlled  by  the  boiler  stop  valve,  which  thus  provides  for  the 
regulation  of  the  supply  of  steam  to  the  engine,  and  for  closing 
the  boiler  off  entirely  from  the  main  steam  pipe  if  necessary. 
The  usual  type  of  valve  employed  is  shown  in  Fig.  82,  and  con- 
sists of  a  valve  disc  guided  to  its  seat  by  wings,  and  raised  or 
lowered  by  its  connection  with  the  screw  spindle  and  handle  as 
shown.  As  also  shown  in  the  figure  the  valve  seat  with  wings 
and  guide  for  the  valve  is  very  commonly  a  separate  piece  of  gun 
metal  or  bronze,  specially  fitted  for  its  strength  and  wearing 
qualities. 

Commonly  in  warship  practice,  and  to  some  extent  in  mer- 
cantile practice,  such  valves  are  made  self-closing  in  case  of 
rupture  of  the  boiler.  In  fundamental  principle  such  a  valve  is 
a  form  of  non-return  valve,  as  illustrated  by  the  check  valve  of 
Fig.  83.  The  screw  stem  does  not  open  the  valve,  but  limits 
simply  the  extent  to  which  the  valve  can  open.  A  second  plain 
stem  passing  through  the  first  then  allows  of  the  valve  being 
pulled  open  by  hand,  even  if  there  is  no  definite  difference  of 
pressure  to  force  it  open.  In  case  of  accident  which  reduces 


BOILERS. 


119 


the  pressure  back  of  the  valve  so  that  the  rush  of  steam  is  in 
the  reverse  direction  to  its  usual  flow,  the  valve  will  be  closed  by 
this  rush  and  held  securely  on  its  seat  by  the  excess  of  pressure 
on  its  outer  face,  thus  shutting  off  the  injured  boiler,  and  retain- 
ing the  others  intact  for  use.  If  such  an  arrangement  is  not 
fitted  and  the  valve  cannot  be  closed  by  hand,  or  until  it  can  be 
thus  closed,  an  entire  battery  of  boilers  may  be  thrown  out  of 


Fig.  82.     Boiler  Main  Stop  Valve. 


use  by  the  rupture  of  any  one  of  them,  all  of  the  steam  formed 
escaping  through  the  one  opening.  Such  form  of  valve  should 
be  placed  with  the  spindle  horizontal,  so  that  its  own  weight 
may  not  enter  as  a  direct  factor  in  the  movement  of  the  valve 
toward  and  from  its  seat. 

In  warships,  where  the  pipes  or  boilers  may  be  pierced  by 
the  fragments  of  exploding  shell,  such  a  safety  provision  may  be 
of  the  utmost  importance  and  value. 


120 


PRACTICAL   MARINE   ENGINEERING. 


[4]  Dry-Pipe,  or  Internal  Steam  Pipe. 

This  is  a  pipe  of  relatively  thin  metal  placed  within  the 
boiler,  extending  lengthwise,  and  close  to  the  top  of  the  shell. 
At  the  inner  end  it  is  closed,  and  at  the  outer  end  connects  with 
the  pipe  leading  to  the  safety  valve  chamber,  stop-valve  and 
boiler  steam  pipe.  Along  the  top  of  the  pipe  are  cut  a  large 
number  of  narrow  slits,  through  which  the  steam  enters  the 


Fig. 


Boiler  Check  Valve. 


pipe.  This  arrangement  has  the  effect  of  drawing  the  steam 
from  the  highest  part  of  the  steam  space,  and  of  straining  out 
some  part  of  the  entrained  water.  A  small  hole  in  the  bottom 
of  the  pipe  provides  for  draining  off  the  water  which  may  grad- 
ually collect. 

The  uniform  draft  of  steam  from  the  whole  length  of  the 
boiler  tends  also  to  prevent  the  priming  which  might  be  caused 
by  drawing  it  all  from  one  point. 


BOILERS. 


121 


[5]  Feed  Check  Valve  and  Internal  Feed  Pipe. 

The  water  from  the  feed  pump  conies  to  the  boiler  through 
the  feed  pipe,  and  then  at  the  boiler  passes  through  the  feed- 
check.  This  is  a  screw-down,  non-return  valve,  as  shown  in 
Fig.  83.  The  valve  itself  is  entirely  disconnected  from  the 
spindle,  and  the  latter  simply  limits  the  height  to  which  the  valve 
can  rise,  while  by  screwing  down  sufficiently,  the  valve  may  be 
forced  shut  and  held  there.  This  construction  is  adopted  so 
that  should  the  feed  pump  stop  working  or  between  the  strokes 
of  the  pump  there  may  be  no  escape  of  water  backward  from 
the  boiler  into  the  pipe.  Two  such  check  valves  are  usually 


Fig.  84.     Combined    Check   and   Stop   Valve. 


fitted  to  each  boiler,  one  connecting  with  the  main  and  the  other 
with  the  auxiliary  feed  pumps. 

In  modern  practice  a  stop  valve  is  usually  fitted  between 
the  check  valve  and  boiler,  in  order  that,  if  necessary  for  ex- 
amination or  repair,  the  check  may  be  shut  off  from  communi- 
cation with  the  boiler.  Such  combined  stop  and  check  valves 
are  frequently  fitted  in  a  single  casing,  the  stop  valve,  of  course, 
being  placed  next  the  boiler  (see  Fig.  84.) 

After  passing  through  the  check-valve  the  water  enters  the 
internal  feed  pipe,  by  which  it  is  led  to  the  point  or  points  of 
delivery.  The  end  of  the  pipe  is  usually  closed,  and  the  water 
is  delivered  through  a  large  number  of  small  holes  distributed 


122 


PRACTICAL   MARINE   ENGINEERING. 


along  the  pipe.  The  delivery  is  usually  below  the  water  level, 
and  often  between  the  nests  of  tubes  where  it  meets  with  the 
rising  currents  of  water  heated  by  them.  In  some  cases  it  is 
led  to  the  bottom  of  the  boiler,  where  it  mixes  with  the  rela- 
tively cool  water  there  found;  but  this  plan  cannot  be  recom- 
mended, as  it  retards  rather  than  assists  circulation.  In  some 
cases  also  the  water  has  been  introduced  as  a  spray  into  the 
steam  space,  but,  while  this  plan  has  some  advantages,  it  has 
not  met  with  general  favor. 


Fig.  85.    Blow-off   Cock. 

In  water-tube  boilers  the  feed  water  is  usually  fed  into  the 
upper  drum,  whence  it  joins  the  circulation  in  the  boiler  as 
noted  in  the  description  of  boilers  of  this  type. 

[6]  Surface  and  Bottom  Blows. 

Cocks  or  valves  and  connecting  pipes  are  fitted  for  blow- 
ing grease  and  scum,  or  mud  sediment  and  water,  out  of  the 
boiler  into  the  sea — Fig.  85.  The  surface  blow  consists  of  a 
valve  or  cock  attached  to  an  internal  pipe  lying  just  below  the 
normal  water  level,  and  either  perforated  with  holes  or  leading 
to  a  shallow  open  pan.  Outside  the  boiler  there  is  a  discharge 
pipe  leading  to  an  outboard  valve,  through  which  the  discharge 
is  effected.  The  scum  and  grease  which  collect  on  the  surface  of 


BOILERS.  123 

the  water  may  by  means  of  this  arrangement  be  blown  out  of  the 
boiler,  and  thus  disposed  of.  In  early  engineering  practice  the 
bottom  blow  was  of  great  importance,  as  it  was  used  not  only  to 
discharge  mud  and  sediment,  but  also  the  relatively  dense  water 
in  the  boiler  when  blowing  down  to  reduce  concentration,  or 
when  emptying  the  boiler  of  water  for  purposes  of  examination 
or  cleaning.  In  modern  practice  with  the  surface  condenser 
and  the  evaporator,  blowing  off  to  reduce  concentration  is  no 
longer  necessary,  and  blowing  the  water  out  of  a  boiler  with 
its  own  steam  is  no  longer  considered  good  practice.  The 
preferable  plan  is  to  allow  the  steam  to  condense  and  the  water 
to  cool  down,  and  to  then  run  it  into  the  bilge  or  remove  it  by 
pump  connections  suitably  arranged.  Due  to  these  facts,  bot- 
tom blow  valves  have  been  sometimes  omitted.  There  may 
still,  however,  be  occasion  to  use  such  valves  for  the  discharge 
of  mud  and  sediment,  and,  therefore,  they  are  still  quite  gen- 
erally fitted.  In  any  event,  there  should  be  some  valve  and  pipe 
connected  with  the  lowest  part  of  the  boiler,  and  through  which 
it  can  be  emptied  in  one  way  or  another. 

Both  surface  and  bottom  blows  are  usually  fitted  to  water- 
tube  boilers,  especially  to  those  types  consisting  of  upper  and 
lower  drums  with  sets  of  connecting  tubes.  The  surface  blow 
is  for  scum  and  grease,  while  the  bottom  blow  is  essentially  for 
mud  and  sediment,  and  is  often  attached  to  a  special  mud-drum 
provided  to  collect  such  substances. 

In  many  cases  the  inner  end  of  the  surface  blow  pipe  ter- 
minates in  a  shallow  pan  located  near  the  low  water  level  in  the 
boiler.  The  water  within  this  pan  will  tend  to  remain  more 
quiet  than  that  outside,  and  the  scum  and  impurities  will  thus 
collect  therein,  ready  for  removal  by  the  use  of  the  blowv  The 
arrangement  thus  serves  as  a  collecting  pan  for  the  surface 
blow,  and  by  most  engineers  is  believed  to  be  quite  efficient  for 
the  purpose  in  view. 

In  other  cases  the  pipe  terminates  in  a  closed  end  and  is 
provided  with  a  number  of  longitudinal  slits  through  which  the 
scum  is  drawn  from  the  surface  of  the  water. 

The  cross-sectional  area  of  the  bottom  blow  may  be  so 
proportioned  as  to  give  about  one  square  inch  for  every  5  tons 
of  water  contained  by  the  boiler,  with  perhaps  somewhat  larger 
area  in  the  case  of  small  boilers.  The  area  for  the  surface  blow 
may  be  usually  made  from  y2  to  1-3  that  of  the  bottom  blow. 


124 


PRACTICAL   MARINE   ENGINEERING. 


[7]  Steam  Gauges. 

The  steam  pressure  within  the  boiler,  or  rather  the  excess 
of  the  pressure  within  over  the  atmospheric  pressure  without, 
is  shown  by  some  form  of  steam  gauge,  of  which  the  best-known 
and  most  used  are  those  employing  a  Bourdon  tube.  In  Fig.  86 
is  shown  such  a  gauge  and  tube,  the  cross  section  of  the  latter 


Fig.  86.     Bourdon   Steam  Gauge. 

being  an  ellipse  as  shown.  When  the  inside  of  the  tube  is  sub- 
jected to  the  pressure  of  the  steam  it  tends  to  become  round  in 
section,  and  as  a  result  of  this  the  tube  as  a  whole  tends  to 
straighten  out.  This  carries  the  free  end  outward,  and  this 
movement,  by  means  of  suitable  connections,  is  made  to  give 
motion  to  the  needle.  These  gauges  are  graduated  by  compari- 
son with  a  mercury  column  or  other  form  of  gauge  tester,  or 
with  a  standard  gauge  which  has  been  thus  graduated.  Steam 
should  not  be  allowed  to  enter  these  gauges,  as  the  change  in 
temperature  may  affect  the  accuracy  of  the  reading.  To  pre- 


BOILERS. 


125 


vent  this  the  pipe  leading  to  the  gauge  is  always  provided  with 
a  loop  or  U  bend,  called  a  "goose  neck,"  which  serves  as  a  trap 
for  the  water  condensed  beyond  this  point.  In  this  way  the 
Bourdon  tube  and  part  of  the  connecting  pipe  are  kept  filled 
with  water,  which  in  turn  is  acted  on  by  the  steam,  and  thus  the 
pressure  is  indicated  without  the  actual  presence  of  steam  within 
the  gauge.  Steam  gauges  require  comparison  with  a  standard 
gauge  from  time  to  time,  in  order  to  make  sure  that  their  indi- 
cations are  correct.  They  are  often  provided  in  duplicate,  and 


Fig.  87.    Water  Gauges. 

frequently  one  gauge,  at  least,  is  provided  of  sufficient  range  to 
allow  of  use  in  the  hydrostatic  boiler  test. 

[8]  Water  Gauge  and  Cocks. 

The  level  of  the  water  within  the  boiler  is  shown  by  a  ver- 
tical glass  tube  connected  to  fittings  at  each  end,  which  in  turn 
connect  the  one  with  the  steam  space  and  the  other  with  the 
water  space.  As  shown  in  Fig.  870,  the  entire  arrangement  of 
glass  and  fittings  is  attached  to  a  hollow  mounting  called  the 
stand-pipe,  water-column,  or  water-gauge  mounting.  To  the  top 
and  bottom  of  this  are  attached  pipes,  one  leading  to  the  steam 
space  at  or  near  the  top,  and  the  other  to  the  water  space  at  or 
near  the  bottom.  In  conne.cting  the  pipe  with  the  steam  space 
care  must  be  taken  that  the  opening  is  not  near  a  steam  outlet, 
as  the  rush  of  steam  past  such  an  opening  might  disturb  the 


126  PRACTICAL   MARINE   ENGINEERING. 

pressure  and  render  the  indications  inaccurate  by  showing  a 
higher  level  of  water  in  the  glass  than  actually  exists  in  the 
boiler.  At  the  bottom  of  the  mounting  a  drain  cock  and  pipe 
are  provided,  so  that  the  glass  may  be  blown  through  and 
cleaned  as  occasion  requires.  Screw  plugs  are  also  fitted  above 
and  below  in  a  line  with  the  base  of  the  tube,  so  that  if  necessary 
a  wire  and  swab  may  be  run  through  the  glass.  Instead  of  the 
connections,  as  shown  in  Fig.  870,  and  which  are  to  be  considered 
as  preferable,  the  ends  of  the  water  column  are  sometimes  con- 
nected by  horizontal  passages  directly  to  the  boiler,  as  in  Fig. 
8/b,  which  shows  the  fitting  attached  to  the  curved  shell  of  boiler. 
With  such  a  mounting  the  level  of  water  in  the  glass  is  more 
liable  to  fluctuation  and  disturbance  due  to  rolling  of  the  ship 
or  to  priming  than  with  the  arrangement  of  a. 

Gauge  glasses  are  usually  from  12  to  15  in.  in  length,  and 
y%  to  J4  in.  diameter.  Due  to  the  fluctuations  in  temperature 
and  the  accompanying  expansion  and  contraction,  they  are 
liable  to  occasional  breakage.  To  avoid  danger  or  trouble  from 
the  escaping  jet  of  water  and  steam,  it  is  quite  customary  in 
modern  practice  to  fit  the  connection  carrying  the  ends  of  the 
glass  with  ball  non-return  valves,  working  on  a  similar  principle 
with  the  safety  stop  valve  described  above.  So  long  as  the 
glass  is  in  place  and  the  pressure  equalized,  the  balls  by  their 
weight  remain  away  from  the  seat  and  leave  the  passages  open. 
Upon  the  breakage  of  the  glass,  however,  they  are  carried  by 
the  rush  of  water  and  steam,  each  against  its  seat,  thus  closing 
the  openings  and  stopping  the  escaping  jets  of  water  and 
steam. 

In  addition  to  the  gauge  glass,  small  cocks,  three  or  four  in 
number,  are  usually  provided.  In  some  cases  such  cocks  are 
attached  to  the  mounting,  and  in  other  cases  to  the  boiler  itself. 
These  cocks  serve  as  a  check  on  the  gauge  glass,  or  for  use  in 
case  the  glass  is  not  to  be  depended  upon.  The  glass  is  usually 
so  adjusted  that  when  the  water  is  at  the  bottom  it  is  still  some 
3  or  4  in.  above  the  level  of  the  highest  heating  surface.  The 
water  cocks  cover  about  the  same  vertical  distance,  though  in 
some  cases  the  lowest  cock  is  placed  nearly  on  a  level  with  the 
top  of  the  heating  surface.  On  single-end  boilers  two  such 
water  gauges  are  often  fitted,  one  on  either  side  at  the  front,  and 
with  water  cocks  at  the  back.  Similarly  on  double-end  boilers 
three  would  be  fitted,  two  on  one  end  and  one  on  the  other. 


BOILERS. 


127 


i  9 1  Hydrokineter. 

This  is  an  appliance  used  to  force  the  circulation  of  the 
water  in  the  boiler,  more  especially  when  raising  steam.  It  con- 
sists, as  shown  in  Fig.  89,  of  a  steam  jet  and  series  of  nozzles 


Fig.  88.    Hydrokineter. 

with  frame  perforated  at  the  back  for  the  entrance  of  water. 
The  steam  is  furnished  from  another  boiler,  and  by  its  inducing 
action  a  current  of  water  is  set  up  and  driven  along,  as  shown  by 
the  arrows.  This  arrangement  is  placed  near  the  bottom  of  the 
boiler,  and  thus  serves  to  drive  out  the  cold  water  which  tends 
to  collect  there,  and  which  is  only  slowly  heated  by  the  opera- 
tion of  natural  circulation. 

[10]  Hydrometer. 

The  density  of  the  water  in  the  boiler  is  determined  by  an 
instrument  known  as  the  hydrometer,  and  shown  in  Fig.  90.      It 


c     I  II  II  II  II 


Fig. 


Hydrometer. 


may  be  of  either  glass  or  metal,  and  consists  essentially  of  two 
bulbs  with  stem  as  shown.  The  upper  and  larger  bulb  is  filled 
with  air,  and  serves  to  give  buoyancy  to  the  instrument; 
while  the  lower  and  smaller  bulb  is  weighted  and  keeps  it  in  the 


128  PRACTICAL   MARINE   ENGINEERING. 

upright  position.  When  a  body  floats  freely,  wholly  or  partly 
immersed  in  a  liquid,  the  weight  of  the  body  equals  the  weight 
of  the  liquid  displaced.  Hence,  in  this  case  the  denser  the  water 
the  less  the  volume  displaced,  and  the  higher  the  stem  out  of 
water.  Average  sea  water  contains  about  i  part  in  32  of  solid 
matter,  and  hydrometers  are  usually  graduated  relative  to  this 
as  a  unit.  That  is,  2  means  twice  as  much  solid  matter  relative- 
ly as  sea  water ;  3,  three  times  as  much,  etc.,  while  o,  of  course, 
means  fresh  water'.  The  density  of  water  depends,  furthermore, 
on  its  temperature,  so  that  the  scale  on  the  hydrometer  can  only 
be  used  with  the  temperature  for  which  it  was  graduated.  This 
is  usually  200  deg.  F.,  though  frequently  three  scales  are  pro- 
vided; for  190  deg.,  200  deg.  and  210  deg.,  respectively.  The 
water  is  drawn  from  the  boiler  through  an  appropriate  pipe  and 
connections  into  a  deep,  slender  vessel  called  a  salimometer  pot. 
Soon  after  drawing,  the  water  cools  down  through  the  tempera- 
ture corresponding  to  the  hydrometer  scales,  and  thus  its  den- 
sity is  observed. 

[11]  Boiler  Saddles. 

The  weight  of  the  boiler  is  supported  on  saddles,  or  bearers, 
which  in  turn  are  attached  to  the  structure  of  the  ship.  A 
modern  form  of  boiler  saddle  is  shown  in  Fig.  90,  and  consists 


Fig.  90.     Boiler  Saddle. 

of  two  or  more  supports  on  each  side  of  the  boiler  of  the  lorm 
shown,  and  extending  each  one  for  some  little  distance  longi- 
tudinally. An  older  form  shown  in  Fig.  91  consists  of  a  plate 
on  edge  connected  with  the  structure  of  the  ship,  extending 
transversely  under  the  boiler,  and  cut  out  to  fit  the  round  of  the 


BOILERS. 


129 


shell.  The  upper  edge  of  this  plate  is  fitted  with  angle  irons  on 
one  or  both  sides  to  give  a  broader  surface  of  support  for  the 
boiler.  The  form  of  saddle  shown  in  Fig.  90  gives  a  better 
longitudinal  support,  and,  moreover,  makes  access  and  exam- 
ination of  the  bottom  of  the  boiler  more  easy  than  with  the  other 


I 

Fig.  91.    Boiler  Saddle. 

form.     Single-end  boilers  usually  have  two  such  saddles  on  each 
side,  while  double-end  boilers  are  given  three  or  four. 

In  addition,  the  boiler  is  held  in  place  in  its  saddles  by  stays 
adjustable  by  screw  turnbuckles,  or  by  other  like  means.  A 
knee-piece,  or  chock,  is  also  often  riveted  to  the  structure  of  the 
ship,  projecting  just  above  the  end  of  the  boiler  at  the  bottom, 
and  thus  preventing  endwise  motion. 

[la]  Boiler  Jigging. 

To  prevent  loss  of  heat  by  radiation  the  boiler  is  covered 
with  non-conducting,  non-combustible  felting,  which  in  turn  is 
held  on  by  iron  straps,  or  in  some  cases  by  a  complete  covering 
of  sheet  metal.  This  covering  is  known  as  boiler  lagging. 

Sec.  18.    DRAFT. 

Draft  is  due  to  a  difference  in  pressure  between  the  uptakes 
or  base  of  the  stack,  and  the  ashpits.  Due  to  this  difference  the 
air  is  driven  up  through  the  grate,  thus  supplying  the  amount  re- 
quired for  combustion,  see  Sec.  u  [2].  We  must  first  inquire 
what  it  is  that  causes  this  difference  of  pressure.  To  make  the 
case  simple  let  AB  Fig.  92,  denote  a  grate  with  burning  fuel,  and 
ACDB  the  funnel.  Then  the  pressure  downward  on  the  top  of 
the  fuel  will  be  equal  to  the  weight  of  a  column  of  air  and  gas 
of  cross  section  equal  to  AB,  and  extending  up  to  the  limits  of 


PRACTICAL  MARINE  ENGINEERING. 


the  atmosphere.  The  pressure  upward  at  the  bottom  of  the 
grate  will  be  the  regular  pressure  of  the  external  air,  and  this 
will  equal  the  weight  of  a  column  of  air  of  the  same  cross-sec- 


Fig.  92.    Showing  Principle  of  Natural 
Draft. 


ig-  93-     Draft  Gauge. 


tion  GH,  and  extending  also  up  to  the  limit  of  the  atmosphere. 
The  difference  in  the  weight  of  these  two  columns  is  seen  to  lie 
in  their  lower  ends,  the  bottom  of  one  being  composed  of  hot 
gas  and  the  other  of  common  air.  The  difference  in  pressure 
will,  therefore,  equal  the  difference  in  weight  between  the  col- 
umn of  hot  gas  CDBA,  and  that  of  air  EFHG.  Actually  the 
column  of  liot  gas  will  extend  some  distance  above  the  top  of 
the  funnel  before  losing  its  heat  or  mingling  with  the  air,  so  that 
the  real  height  of  the  column  is  greater  than  the  funnel.  This 
difference  is,  however,  usually  neglected,  and  the  difference  in 
pressure  is  usually  taken  as  the  difference  in  weight  between  the 
column  of  hot  gas  extending  from  the  grates  to  the  top  of  the 
funnel,  and  a  like  column  of  external  air.  The  pressure  per 
square  inch  will,  of  course,  be  likewise  equal  to  the  difference 
between  two  similar  columns  of  one  square  inch  section.  This 
shows  the  conditions  for  producing  the  so-called  natural  or  fun- 
nel draft  pressure. 

In  order  that  the  combustion  may  proceed,  however,  it  is 


BOILERS.  131 

not  enough  to  produce  simply  a  column  of  hot  gas.  Care  must 
also  be  taken  to  provide  for  a  free  and  full  inflow  of  the  outside 
air  to  the  grates  in  order  that  the  amount  necessary  for  combus- 
tion may  be  on  hand  as  required. 

Draft  pressures  are  usually  measured  by  an  instrument 
known  as  a  draft  gauge.  As  illustrated  in  Fig.  93,  it  consists 
of  a  bent  U-  tube  partly  filled  with  water  as  shown,  and  with  a 
scale  between  the  legs.  In  use  the  two  legs  are  connected  by 
appropriate  means  to  the  two  places  between  which  the  differ- 
ence of  pressure  is  desired,  as  for  example,  the  ash-pit  and  fun- 
nel-base, or  external  air  and  funnel-base.  In  the  latter  case  one 
leg  is  open  to  the  air  and  the  other  is  connected  by  a  flexible 
pipe  or  other  similar  means  to  the  uptake  or  funnel-base.  With 
equal  pressure  in  both  places  the  water  will  stand  at  the  same 
height  in  both  legs,  but  with  a  difference  of  pressure  it  will  rise 
in  one  leg  and  fall  in  the  other,  the  movement  being  toward  the 
lesser  pressure.  The  difference  in  pressure  is  then  measured  by 
the  weight  of  a  column  of  water  equal  to  the  difference  in  height 
between  the  two  legs.  This  is  usually  read  in  inches,  and  hence 
draft  pressures  are  usually  expressed  in  inches  of  water.  With 
ordinary  funnel  draft  the  pressure  is  usually  from  54  to  ^  or  ^4 
inch,  with  assisted  or  light  forced  draft  from  y2  inch  to  I  inch, 
with  forced  draft  on  large  ships  from  I  to  3  inches,  while  on  fast 
yachts  and  torpedo  boats  the  pressure  may  rise  to  5  or  6  inches 
or  more.  In  this  connection  it  may  be  well  to  remember  that 
an  inch  of  water  pressure  is  equal  to  a  pressure  of  about  2-3  oz. 
per  square  inch. 

Since  as  above  explained,  natural  draft  is  dependent  on  the 
difference  in  weight  between  the  hot  gas  in  the  funnel  and  the 
outside  air,  it  follows  that  the  lighter,  and,  therefore,  the  hotter 
the  gas  the  stronger  the  draft ;  also  the  higher  the  funnel  the 
greater  the  difference  and  the  stronger  the  draft.  A  strong  nat- 
ural draft  with  moderate  height  of  funnel  requires,  therefore, 
a  high  temperature  of  escaping  gases,  and  since  these  carry 
away  heat  to  the  outside  air,  this  means  a  loss  of  heat  and  hence 
of  economy.  Strong  natural  draft  requires,  therefore,  either  a 
very  high  funnel,  or  a  very  high  temperature  of  escaping  gases 
with  the  resulting  loss  in  economy.  The  usual  temperature  of 
the  gases  in  the  funnel  base  is  from  600  cleg,  to  800  deg.  Fah. 
At  a  lower  temperature  the  draft  will  be  very  poor,  while  with 
a  higher  temperature,  the  increase  of  draft  will  be  obtained  at 


132  PRACTICAL  MARINE  ENGINEERING. 

the  expense  of  economy.  With  natural  draft  the  rate  of  com- 
bustion will  usually  range  from  12  or  13  to  20  Ib.  of  coal  per 
square  foot  of  grate  surface,  dependent  on  the  quality  of  the  coal 
and  other  circumstances. 

From  the  preceding  it  is  clear  that  with  natural  or  funnel 
draft  the  power  which  can  be  obtained  from  a  square  foot  of 
grate  surface  soon  reaches  a  limit,  and  under  present  conditions 
this  is  usually  found  at  from  10  to  12  I.  H.  P.  In  order  to  ob- 
tain more  power  per  square  foot  of  grate  area,  or  in  general 
more  per  pound  of  boiler,  some  form  of  assisted  or  forced  draft 
is  necessary.  In  all  cases  where  very  high  speed  is  required  as 
in  torpedo  boats,  fast  launches,  yachts,  etc.,  the  application  of 
forced  draft  is  a  necessity,  as  the  boilers  required  to  develop 
the  power  under  natural  draft  would  occupy  far  more  weight 
and  space  than  could  be  assigned  them.  With  assisted  or  mod- 
erately forced  draft  the  power  per  square  foot  of  grate  surface 
may  be  raised  to  from  15  to  18  I.  H.  P.,  and  if  properly  installed, 
without  sacrifice  of  economy.  Writh  harder  forcing  the  power 
may  be  raised  to  25  or  30  I.  H.  P.  per  square  foot  of  grate  sur- 
face, or  even  more  in  extreme  cases,  but  necessarily  at  the  ex- 
pense of  a  loss  in  economy. 

The  immediate  object  of  all  forced  draft  appliances  is  to  in- 
crease the  difference  in  pressure  between  the  ash-pit  and  uptake 
over  what  it  would  be  with  the  funnel  alone,  at  the  same  time 
taking  care  to  provide  for  the  full  supply  of  air  to  the  grates  as 
required  by  the  rate  of  combustion  desired.  To  this  end  there 
are  four  fairly  distinct  means  as  follows : 

(1)  Closed  fire  room. 

(2)  Closed  ash-pit. 

(3)  Exhaust  fans  in  the  uptakes,  or  between  them  and  the 
funnel. 

(4)  Steam  jets  in  base  of  funnel. 

In  the  closed  fire-room  system  the  air  is  forced  by  means 
of  blowers  into  the  fire-room,  which  is  closed  air  tight  except 
for  the  outlet  into  the  furnaces.  The  fire-room  is  hence  under 
a  pressure  greater  than  the  other  parts  of  the  ship,  and  to  enter 
or  leave  it,  an  air  lock  is  necessary,  as  illustrated  in  Fig.  94. 
Small  air  valves  are  provided  by  means  of  which  the  pressure  in 
the  lock  may  be  equalized  with  that  on  either  side,  as  may  be 
desired,  and  this  being  done  the  door  may  be  opened.  To  leave 
the  fire-room,  for  example,  both  doors  of  the  lock  being  closed, 


BOILERS. 


133 


the  pressure  inside  is  equalized  with  the  fire-room  and  the  door 
being  opened  the  person  enters  and  closes  it  behind.  The  pres- 
sure in  the  lock  is  then  equalized  with  that  outside,  the  door  is 
opened,  and  thus  exit  is  effected.  The  chief  advantages  of  this 
system  lie  in  the  fact  that  the  boilers  are  left  unchanged  as  for 


Fig.  94.    Showing  Principle  of  Air  Lock. 

natural  draft,  and  the  shift  from  one  system  to  the  other  is  read- 
ily made.  The  necessary  structural  arrangements  are  also 
sometimes  more  readily  effected  than  for  the  other  systems,  es- 
pecially in  warship  practice,  and  this  reason  may  in  some  cases 
largely  determine  the  choice.  Its  chief  disadvantages  lie  in  the 
difficulty  of  making  the  fire-rooms  air  tight,  in  the  necessity  of 
fitting  air-locks  as  above  described,  and  in  the  more  severe 
strain  placed  on  the  fire-room  force  than  with  other  systems. 

In  the  closed  ash-pit  system  the  air  is  forced  by  means  of 
blowers  into  conduits  leading  directly  to  the  ash-pits  and  fur- 
naces, which  are  closed  air  tight  from  the  fire-room.  The  latter 
are,  therefore,  under  a  pressure  greater  than  in  the  fire-room, 
and  if  the  furnace,  doors  were  opened  with  the  draft  on,  the 
flames  and  gas  would  be  driven  out  into  the  fire-room.  To  pre- 
vent this  the  draft  must  be  shut  off  when  the  furnace  or  ash-pit 
doors  are  opened,  and  to  avoid  accidents  a  locking  arrangement 
is  often  provided  which  prevents  the  door  from  being  opened 
while  the  draft  is  on,  or  the  draft  from  being  turned  on  till  the 
doors  are  closed.  The  Hotvdcn  forced  draft,  which  is  representa- 
tive of  this  system,  provides  also  for  heating  the  air  by  means 
of  the  waste  furnace  gases  before  it  enters  the  ash-pits  and  fur- 
naces. The  general  arrangement  for  the  Howden  draft  is 
shown  in  Fig.  95.  In  the  uptake  is  fitted  a  nest  of  vertical  tubes 
through  which  the  furnace  gases  pass  on  their  way  to  the  funnel. 
The  air  from  the  blower  is  delivered  into  a  conduit  which  leads 


134 


PRACTICAL  MARINE  ENGINEERING. 


BOILERS.  135 

across  the  front  of  the  boiler  and  within  which  these  tubes  are 
placed,  as  shown  in  the  figure.  The  furnace  gases  pass,  there- 
fore, through  the  tubes  while  the  entering  air  passes  about  them 
on  the  outside,  and  thus  absorbs  a  part  of  their  heat  which  would 
otherwise  escape  through  the  funnel.  The  heated  air  then 
passes  downward  to  a  kind  of  special  front  over  the  ash-pits  and 
furnaces.  From  these  passages  openings  controlled  by  either 
sliding  or  hinged  valves  lead  into  the  ash-pits  and  into  the  fur- 
naces above  the  grates.  The  supply  of  air  to  the  fire  may  thus 
be  regulated,  and  the  relative  amounts  delivered  above  and  be- 
low the  grate  may  be  adjusted  as  required  for  the  best  combus- 
tion. The  ash-pit  and  furnace  doors  are,  of  course,  air  tight  to 
the  fire-room,  and  arrangements  may  be  provided  for  insuring 
the  closure  of  the  valves  before  opening  the  doors  as  above  ex- 
plained. 

Induced  draft  is  represented  by  the  Ellis  and  Eaves  system, 
as  illustrated  in  Fig.  96.  A  large  exhaust  fan  is  so  placed  as  to 
draw  the  gases  along  the  uptakes  and  discharge  them  to  the 
funnel,  thus  producing  the  draft  by  means  of  a  defect  of  pres- 
sure in  the  uptakes,  rather  than  by  an  increase  in  the  ash-pit  or 
fire-room.  Considering  the  uptakes  and  funnel  base  as  repre- 
senting the  main  passage,  the  fan  is  so  placed  as  to  draw  from 
the  former  and  deliver  into  the  latter.  Between  the  inlet  and 
delivery  is  a  slide  or  damper  in  the  main  passage,  while  the  fan 
inlet  may  similarly  be  closed  off.  When  the  blower  is  in  opera- 
tion the  former  of  these  is  closed  while  the  latter  is  open  and 
the  products  of  combustion  are  thus  drawn  from  the  uptake  and 
delivered  to  the  funnel-base  on  the  other  side  of  the  main  slide. 
On  the  other  hand,  if  it  is  desired  to  run  without  the  fan  the 
inlet  may  be  closed  off  and  the  main  slide  or  damper  opened, 
thus  giving  the  usual  arrangement  for  natural  draft. 

The  entering  air  which  in  this  case  is  supplied  either  by  nat- 
ural ventilation  or  by  special  blowers  is  heated  before  reaching 
the  furnaces  usually  by  being  drawn  around  nests  of  tubes 
through  which  the  gases  pass  on  their  way  to  the  fan.  These 
tubes  are  sometimes  arranged  vertically  in  front  of  the  boiler  as 
in  the  Howden  system,  and  as  shown  in  the  figure,  and  some- 
times horizontally  in  the  spandrels  over  or  between  the  boilers. 
The  air  thus  heated  is  then  led  through  passages  at  the  side  of 
the  front  connections  to  the  ash-pits,  and  to  the  spaces  around 
the  furnace  frames.  The  furnace  and  ash-pit  fronts  are  closed 


136 


PRACTICAL  MARINE  ENGINEERING. 


BOILERS.  137 

from  the  fire-room,  and  a  certain  proportion  of  the  air  is  ad- 
mitted above  and  below  the  grates  according  to  the  needs  of  the 
combustion.  This  system  has  the  advantage  of  leaving  the  fire- 
room  open  and  of  working  the  ash-pit  under  practically  atmos- 
pheric pressure.  Furthermore  all  leaks  between  the  fire-room 
and  the  fire  side  of  the  boiler  are  inward,  and  thus  the  fire-room 
is  kept  free  from  escaping  gas,  or  from  flame  and  gas  when  the 
furnace  doors  are  opened.  Its  chief  disadvantage  lies  in  the 
large  size  and  weight  of  fan  necessary  to  handle  the  gases,  as 
compared  with  the  smaller  size  needed  for  the  air  alone  in  the 
closed  fire-room  and  closed  ash-pit  systems. 

The  action  of  steam-jets  in  the  base  of  the  funnel  is  to  pro- 
duce a  defect  of  pressure  in  the  uptake,  thus  giving  a  form  of  in- 
duced draft.  Turning  the  exhaust  of  a  non-condensing  engine 
into  the  funnel  produces  the  same  result,  and  may  also  be  con- 
sidered as  a  form  of  induced  draft.  The  latter  arrangement  is 
sometimes  met  with  in  tugs  and  other  small  craft,  while  the 
steam  jet  is  much  used  throughout  the  whole  range  of  tugs, 
yachts,  launches,  tenders  and  all  forms  of  small  craft.  One  of  the 
special  advantages  of  the  steam  jet  is  its  readiness  for  use  as  soon 
as  a  small  head  of  steam  is  formed,  and  independent  of  any 
special  auxiliary  machinery.  It  is,  however,  a  wasteful  and  ex- 
pensive mode  of  obtaining  increased  combustion,  and  is  only 
to  be  recommended  when  simplicity  and  the  saving  of  weight 
and  space  are  of  more  importance  than  economy  of  steam. 

In  this  connection  it  must  not,  of  course,  be  forgotten  that 
the  operation  of  the  blowers  used  in  the  closed  fire-room,  closed 
ash-pit,  or  induced  systems  of  draft  requires  also  the  consump- 
tion of  steam  and  hence  of  coal,  so  that  in  no  case  can  forced 
draft  be  obtained  without  paying  for  it  in  one  form  or  other. 
General  experience  shows,  however,  that  for  a  given  increase  in 
the  rate  of  combustion,  the  use  of  a  steam  jet  requires  more 
steam  than  blowers,  so  that  the  latter  are  to  be  preferred  except 
in  such  special  cases  as  are  referred  to  above. 

Reference  may  also  be  made  to  the  practice  of  introducing 
jets  of  air  under  considerable  pressure  into  the  combustion 
chambers  or  furnaces  of  steam  boilers.  The  result  of  such  an 
arrangement  is  two  fold : 

(1)  It  places  the  air  at  the  immediate  point  where  it  may 
be  of  the  most  value  in  aiding  to  complete  the  combustion. 

(2)  Its  introduction  under  pressure  insures  its  thorough 


138  PRACTICAL  MARINE  ENGINEERING. 

mingling  with  the  gases  and  the  latter  with  each  other,  and  thus 
still  further  aids  in  bringing  about  the  conditions  necessary  for 
complete  combustion.  The  introduction  of  air  in  this  manner 
has  met  with  considerable  favor  in  many  cases  where  it  has  been 
tried,  especially  in  certain  forms  of  water-tube  boilers  where  the 
volume  available  for  the  combustion  of  the  gases  before  they 
pass  among  the  tubes  is  often  limited  or  insufficient  in  amount. 

Sec.  19.  BOILER  DESIGN  IN  ACCORDANCE  WITH  THE 
RUIZES  OF  THE  TJ.  S.  BOARD  OF  SUPERVISING 
INSPECTORS  OF  STEAM  VESSELS. 

In  the  present  section  extracts  are  given  from  the  United 
States  Rules  relating  to  the  design  of  Marine  boilers.  To  give 
here  the  Rules  entire  would  require  more  space  than  is  avail- 
able, but  those  of  chief  importance  are  given,  though  in  some 
cases  the  wording  is  slightly  changed  to  aid  in  condensation. 

Rivet  Holes  to  be  Drilled. 

All  boilers  built  for  marine  purposes  after  July  i,  1898, 
shall  be  required  to  have  all  the  rivet  holes  "fairly  drilled"  in- 
stead of  punched. 

Pressure  Allowed  on  Cylindrical  Shell  Boilers. 

Rule. — Multiply  one-sixth  (1-6)  of  the  lowest  tensile 
strength  found  stamped  on  any  plate  in  the  cylindrical  shell  by 
the  thickness — expressed  in  inches  or  parts  of  an  inch — of  the 
thinnest  plate  in  the  same  cylindrical  shell,  and  divide  by  the 
radius  or  half  diameter — also  expressed  in  inches — and  the  quo- 
tient will  be  the  pressure  allowable  per  square  inch  of  surface 
for  single  riveting,  to  which  add  20  per  cent  for  double  riveting, 
when  all  the  rivet  holes  in  the  shell  of  such  boiler  have  been 
"fairly  drilled"  and  no  part  of  such  hole  has  been  punched. 

Test  Pressure. 

The  hydrostatic  pressure  applied  must  be  in  the  proportion 
of  150  pounds  to  the  square  inch  to  100  pounds  to  the  square 
inch  of  the  steam  pressure  allowed. 

Butt  Straps. 

Where  butt  straps  are  used  in  the  construction  of  marine 
boilers,  the  straps  for  single  butt-strapping  shall  in  no  case  be 
less  than  the  thickness  of  the  shell  plates;  and  where  double 
butt  straps  are  used,  the  thickness  of  each  shall  in  no  case  be 
less  than  five-eighths  (^)  the  thickness  of  the  shell  plates. 


BOILERS.  139 

Stays  and  'Flat  Surfaces. 

In  allowing  the  strain  on  a  screw  stay  bolt,  the  diameter  of 
the  same  shall  be  determined  by  the  diameter  at  the  bottom  of 
the  thread. 

No  braces  or  stays  hereafter  employed  in  the  construction 
of  boilers  shall  be  allowed  a  greater  strain  than  six  thousand 
(6,000)  pounds*  per  square  inch  of  section,  and  no  solid  or  hol- 
low screw  stay  bolt  shall  be  allowed  to  be  used  in  the  construc- 
tion of  marine  boilers  in  which  salt  water  is  used  to  generate 
steam  unless  said  screw  stay  bolt  is  protected  by  a  socket.  But 
such  screw  etay  bolts  without  socket  may  be  used  in  staying  the 
fire-boxes  and  furnaces  of  such  boilers,  and  elsewhere  when  such 
screw  stay  bolts  are  drilled  at  each  end  with  a  hole  not  less  than 
Y%  inch  diameter  to  a  depth  of  at  least  ]/2  inch  beyond  inside  sur- 
face of  sheet,  when  fresh  water  is  used  for  generating  steam  in 
said  boilers  (to  take  effect  on  and  after  July  I,  1898,  on  all  boil- 
ers contracted  for  or  construction  commenced  on  or  after  that 
date).  Water  used  from  a  surface  condenser  shall  be  deemed 
fresh  water.  The  flat  surface  at  back  connection  or  back  end  of 
boilers  may  be  stayed  by  the  use  of  a  tube,  the  ends  of  which 
being  expanded  in  holes  in  each  sheet  beaded  and  further  se- 
cured by  a  bolt  passing  through  the  tube  and  secured  by  a  nut. 
An  allowance  of  steam  shall  be  given  from  the  outside  diameter 
of  pipe.  For  instance,  if  the  pipe  used  be  il/2  inches  diameter 
outside,  with  a  il/\.  inch  bolt  through  it,  the  allowance  will  be 
the  same  as  if  a  il/2  inch  bolt  were  used  in  lieu  of  the  pipe  and 
bolt.  And  no  brace  or  stay  bolt  used  in  a  marine  boiler  will 
be  allowed  to  be  placed  more  than  iol/2  inches  from  center  to 
center  to  brace  flat  surfaces  on  fire-boxes,  furnaces,  and  back 
connections ;  nor  on  these  at  a  greater  distance  than  will  be 
determined  by  the  following  formulas. 

Flat  surfaces  on  heads  of  boilers  may  be  stiffened  with 
doubling  plate,  tees,  or  angles. 

The  working  pressure  allowed  on  flat  surfaces  fitted  with 
screw  stay  bolts  riveted  over,  screw  stay  bolts  and  nuts,  or  plain 
bolt  with  single  nut  and  socket,  or  riveted  head  and  socket,  will 
be  determined  by  the  following  rule : 

When  plates  7-16  inch  thick  and  under  are  used  in  the  con- 
struction of  marine  boilers,  using  112  as  a  constant,  multiply 


*  This  limit  is  understood  to  refer  only  to  the  use  of  iron  as  a  material. 


140  PRACTICAL  MARINE  ENGINEERING. 

this  by  the  square  of  the  thickness  of  plate  in  sixteenths  of  an 
inch.  Divide  this  product  by  the  square  of  the  pitch  or  dis- 
tance from  center  to  center  of  stay  bolt. 

Plates  above  7-16  inch  thick,  the  pressure  will  be  deter- 
mined by  the  same  rule,  excepting  the  constant  will  be  120.  v 

On  other  flat  surfaces  there  may  be  used  stay  bolts  with 
ends  threaded,  having  nuts  on  same,  both  on  the  outside  and 
inside  of  plates.  The  working  pressure  allowed  would  be  as 
follows : 

A  constant  140,  multiplied  by  the  square  of  the  thickness 
of  plate  in  sixteenths  of  an  inch,  this  product  divided  by  the  pitch 
or  distance  of  bolts  from  center  to  center,  squared,  gives  work- 
ing pressure. 

Flat  part  of  boiler-head  plates  when  braced  with  bolts  hav- 
ing double  nuts  and  a  washer  at  least  one-half  the  thickness  of 
head,  where  washers  are  riveted  to  the  outside  of  the  head,  and 
of  a  size  equal  to  %  of  the  pitch  of  stay  bolts,  or  where  heads 
have  a  stiffening  plate  either  on  inside  or  outside  covering  the 
area  braced,  will  equal  the  thickness  of  head  and  washers,  the 
head  and  stiffening  plate  being  riveted  together  *  *  *  * 
shall  be  allowed  a  constant  of  200,  rivets  to  be  spaced  by  thick- 
ness of  washer  on  the  stiffening  plate.  Boiler  heads  so  rein- 
forced will  be  allowed  a  thickness  to  compute  pressure  allowed 
of  80  per  cent  of  the  combined  thickness  of  head  and  washer,  or 
head  and  stiffening  plate. 

Plates  fitted  with  double  angle  iron  and  riveted  to  plate 
with  leaf  at  least  two-thirds  thickness  of  plate  and  depth  at  least 
one-fourth  of  the  pitch  would  be  allowed  the  same  pressure  as 
determined  by  formula  for  plate  with  washer  riveted  on. 

But  no  flat  surface  shall  be  unsupported  at  a  greater  dis- 
tance in  any  case  than  16  inches,  and  such  flat  surfaces  shall 
not  be  of  less  strength  than  the  shell  of  the  boiler,  and  able  to 
resist  the  same  strain  and  pressure  to  the  square  inch. 

Steel  stay  bolts  of  a  diameter  of  ij4  inches  and  not  ex- 
ceeding a  diameter  of  2^  inches  at  the  bottom  of  the  thread 
may  be  allowed  a  strain  not  exceeding  8,000  pounds  per  square 
inch  of  cross-section.  Steel  stay  bolts  exceeding  a  diameter 
of  2y2  inches  at  bottom  of  thread  may  be  allowed  a  strain  not 
exceeding  9,000  pounds  per  square  inch  of  cross-section,  but  no 
forged  or  welded  steel  stays  will  be  allowed. 

Any  steel  stay  brace  of  the  Huston  type,  or  similar  thereto, 


BOILERS.  141 

prepared  at  one  heat  from  a  solid  piece  of  plate  without  welds, 
intended  for  use  in  marine  boilers,  to  be  allowed  a  strain  ex- 
ceeding 6,000  pounds  per  square  inch  of  cross-section,  shall  be 
tested  as  hereinafter  provided  for  steel  bars  intended  to  be  used 
as  stay  bolts ;  and  any  brace  formed  in  this  way,  with  an  area 
of  cross-section  of  1.227  and  not  exceeding  an  area  of  5  inches, 
may  be  allowed  a  strain  not  exceeding  7,000  pounds  per  square 
inch  of  cross-section ;  exceeding  this  area,  may  be  allowed  a 
strain  not  exceeding  8,000  pounds  to  the  square  inch. 

All  steel  bars  intended  for  use  as  stay  bolts  to  be  allowed 
a  strain  exceeding  6,000  pounds  per  square  inch  of  cross-section 
shall  be  tested  by  the  inspectors,  in  lots  not  to  exceed  fifty  bars, 
in  the  following  manner :  Inspectors  shall  promiscuously  select 
one  bar  from  each  lot  and  bend  one  end  of  such  bar  cold  to  a 
curve,  the  inner  radius  of  which  is  equal  to  one  and  one-half 
times  the  diameter  of  the  test  bar ;  and  should  any  such  test  bar 
break  in  the  bending  process  the  lot  from  which  the  bar  was 
taken  shall  not  be  allowed  to  be  worked  into  stay  bolts  for  mar- 
ine boilers. 

Corrugated  Furnace  Flues. 

Corrugated  furnace  flues  constructed  with  corrugations  8 
inches  from  center  to  center,  the  radius  of  outer  corrugation 
being  not  more  than  one-half  of  the  reverse  or  suspension  curve, 
the  plain  parts  of  the  ends  not  exceeding  9  inches  in  length, 
made  of  plates  not  less  than  five-sixteenths  of  an  inch  thick, 
when  new,  corrugated  with  practically  true  circles,  shall  be 
allowed  a  steam  pressure  in  accordance  with  the  following 
formula : 

Pressure  in  pounds 

Where  T  =  thickness  in  inches. 

D  =  mean  diameter,  in  inches. 

The  strength  of  all  corrugated  flues,  other  than  described 
in  the  preceding  paragraph,  when  used  for  furnaces  or  steam 
chimneys  (corrugation  not  less  than  il/2  inches  deep,  and  not 
exceeding  8  inches  from  centers  of  corrugation)  and  provided 
that  the  plain  parts  at  the  ends  do  not  exceed  9  inches  in  length 
and  the  plates  are  not  less  than  five-sixteenths  inch  thick  when 
new,  corrugated,  and  practically  true  circles,  to  be  calculated 
from  the  following  formula : 


i42  PRACTICAL  MARINE  ENGINEERING. 

14000  X  T  =  pressure. 

T  =  thickness,  in  inches. 

D  =  mean  diameter,  in  inches. 

Ribbed  Furnace  Flues. 

The  strength  of  ribbed  flues,  when  used  for  furnaces  or 
steam  chimneys  (rib  projections  not  less  than  i^  inches  deep), 
and  not  more  than  9  inches  from  center  to  center  of  ribs,  and 
provided  that  the  plain  parts  at  ends  do  not  exceed  9  inches, 
and  constructed  of  plates  not  less  than  seven-sixteenths  inch 
thick,  with  practically  true  circles  ;  and 

The  strength  of  corrugated  flues,  when  used  for  furnaces 
or  steam  chimneys,  corrugated  by  sections  with  flanged  ends 
overlapping  each  other  and  riveted  with  ^4  inch  rivets,  2  inch 
pitch,  corrugated  projection  not  less  than  2y2  inches  from  inside 
of  flue  to  outside  of  lap,  and  not  more  than  18  inches  between 
centers  of  corrugation,  provided  plain  parts  at  ends  do  not  ex- 
ceed 12  inches  in  length,  constructed  of  plates  not  less  than  7-16 
inch  thick,  with  practically  true  circles  ;  and 

The  strength  of  ribbed  flues,  when  used  for  furnaces  or 
steam  chimneys,  when  made  in  sections  of  not  less  than  12 
inches  in  length,  measuring  from  center  to  center  of  said  pro- 
jections, and  flanged  to  a  depth  not  exceeding  2^  inches,  and 
substantially  riveted  together  with  wrought-iron  rings  between 
such  flanges,  and  such  rings  have  a  thickness  of  not  less  than 
double  the  thickness  of  the  material  in  the  flue,  and  a  depth  not 
less  than  2^  inches,  when  straight  ends  do  not  exceed  12  inches 
in  length,  shall,  in  each  of  the  above  cases,  be  calculated  from 
the  following  formula : 

C  =  14000,  a  constant. 

T  =  thickness  of  flue  in  decimals  of  an  inch. 

D  =  diameter  of  flue  in  inches. 

P  =  pressure  of  steam  allowable. 

C  x  T 

Formula  :  P    =  — ^. — 

When  plain  horizontal  flues  are  made  in  sections  of  less 
than  8  feet  in  length  and  flanged  to  a  depth  of  not  less  than 
2 1/2  inches,  and  substantially  riveted  together  with  wrought-iron 
rings  between  such  flanges,  and  such  rings  have  a  thickness  of 
not  less  than  half  an  inch  and  a  width  of  not  less  than  2^  inches, 


BOILERS.  143 

or,  in  lieu  thereof,  angle-iron  rings  are  employed,  and  such  rings 
have  a  thickness  of  material  of  not  less  than  double  the  thick- 
ness of  the  material  in  the  flue  and  a  depth  of  not  less  than  2l/2 
inches,  and  substantially  riveted  in  position  with  wrought-iron 
thimbles  between  the  inner  surface  of  the  ring  and  the  outer  sur- 
face of  the  flue,  at  a  distance  from  the  flue  not  to  exceed  2 
inches,  with  rivets  having  a  diameter  of  not  less  than  one  and 
one-half  times  the  thickness  of  the  material  in  the  flue,  and 
placed  apart  at  a  distance  not  to  exceed  6  inches  from  center 
to  center  at  the  outer  surface  of  the  flue,  the  distance  between 
the  flanges,  or  the  distance  between  such  angle-iron  rings,  shall 
be  taken  as  the  length  of  the  flue  in  determining  the  pressure 
allowable,  which  pressure  shall  be  determined  in  accordance 
with  the  following  formula : 

89600  X  T2 


P  = 


L  X  D 


Where  P  =  pressure  of  steam  allowable  in  pounds. 
T  =  thickness  of  flue  in  decimals  of  an  inch. 
L  =  length  of  section  in  feet. 
D  =  diameter  of  flue  in  inches. 

All  vertical  boiler  furnaces  constructed  of  wrought  iron  or 
steel  plates,  and  having  a  diameter  of  over  42  inches  or  a  height 
of  over  40  inches,  and  crown  sheets  of  flat-sided  furnaces,  if 
made  with  a  radius  of  over  21  inches,  and  all  cylindrical  shells  of 
back  connections  having  a  radius  of  over  21  inches,  shall  be 
stayed  as  provided  *****  for  flat  surfaces.  But  the 
cylindrical  shell  or  bottom  of  back  connections  may  be  stiff- 
ened by  angles  or  tees  secured  with  rivets  spaced  no  more  than 
6  inches  from  center  to  center,  the  distance  from  center  of 
rivets  at  edge  to  center  of  tee,  or  from  center  to  center  of  tees, 
not  to  exceed  24  inches,  tees  and  rivets  to  be  of  suitable  section 
for  the  pressure  and  radius  of  surface  braced.  And  the  thick- 
ness of  material  required  for  the  shells  of  such  furnaces  shall  be 
determined  by  the  distance  between  the  centers  of  the  stay  bolts 
in  the  furnace  and  not  in  the  shell  of  the  boiler ;  and  the  steam 
pressure  allowable  shall  be  determined  by  the  distance  from 
center  of  stay  bolts  in  the  furnace,  and  the  diameter  of  such  stay 
bolts  at  the  bottom  of  the  thread.  Where  steam  chambers  are 
formed  in  such  vertical  boilers  at  the  upper  end  thereof  by  a 
sheet  in  form  of  a  cone  between  the  upper  tube  sheet  and  upper 


144  PRACTICAL  MARINE  ENGINEERING. 

head  of  such  boiler,  the  pressure  allowed  shall  be  determined  by 
the  diameter  of  such  cone  at  the  central  point  between  the  tube 
sheet  and  upper  head  of  such  boiler. 

Steam  chimneys  or  superheaters  formed  of  a  flue,  with  an 
inclosing  shell,  shall  be  built  as  follows : 

The  outer  shell  subject  to  internal  pressure  shall  be  con- 
structed under  rules  governing  the  shells  of  boilers,  without  al- 
lowance for  any  bracing  to  lining  or  flue. 

For  lanings. 

The  lining  of  flue  subject  to  external  pressure  shall  be  con- 
structed as  follows : 

Plates  under  30  inches  in  diameter  shall  be  at  least  5-16 
inch  thick. 

Thirty  inches  and  under  45  inches  diameter,  plates  shall  be 
at  least  ^  inch  thick. 

Forty-five  inches  and  under  55  inches  diameter,  plates  shall 
be  at  least  7-16  inch  thick. 

Fifty-five  inches  and  under  65  inches  diameter,  plates  shall 
be  at  least  J^  inch  thick. 

Sixty-five  inches  and  under  75  inches  diameter,  plates  shall 
be  at  least  9-16  inch  thick. 

Seventy-five  inches  and  under  85  inches  diameter,  plates 
shall  be  at  least  y%  inch  thick. 

Eighty-five  inches  diameter  a  corresponding  increase  in 
thickness  of  plate  of  1-16  inch  for  every  10  inches  increase  in 
diameter. 

The  linings  of  flues  shall  be  braced  as  follows : 

On  or  for  all  boilers  using  salt  water,  carrying  a  steam  pres- 
sure of  60  pounds  and  under  per  square  inch,  the  lining  shall  be 
braced  with  socket  bolts,  with  heads,  and  with  ends  of  bolts 
threaded  for  nuts,  with  plate  washers  not  over  12  inches  be- 
tween centers  (or  equivalent)  on  the  inside  of  the  lining;  bolts 
to  be  at  least  I  inch  diameter. 

On  or  for  all  boilers  using  salt  water,  carrying  a  steam  pres- 
sure over  60  pounds  per  square  inch,  the  lining  shall  be  braced 
with  socket  bolts,  with  heads,  and  with  ends  of  said  bolts  thread- 
ed for  nuts,  with  plate  washers  not  over  10  inches  between  cen- 
ters (or  equivalent)  on  the  inside  of  lining;  bolts  to  be  at  least 
ij^j  inch  diameter,  the  diameter  of  the  bolts  to  be  determined  by 
the  diameter  at  the  bottom  of  the  thread  of  said  bolts. 

On  or  for  all  boilers  using  fresh  water,  the  lining  may  be 


BOILERS.  145 

braced  as  described  for  boilers  using  salt  water,  or  as  hereafter 
described  (or  equivalent  thereto),  viz.,  with  iron  or  steel  angle 
rings,  properly  riveted  to  lining,  and  properly  connected  to 
outer  shell  by  plate  braces.  These  plate  braces  shall  be  of  suffi- 
cient number  and  width  to  make  space  between  plates  not  over 
20  inches  on  the  lining;  the  angle  rings  shall  be  at  least  2l/2 
inches  by  2l/2  inches  on  lining,  5-16  inch  and  $£  inch  thick; 

3  inches  by  3  inches  on  linings,  7-16  inch  and  y2  inch  thick  ;   3^ 
inches  by  3^  inches  on  linings,  9-16  inch  and  ^  inch  thick,  and 

4  inches  by  4  inches  on  linings,  11-16  inch  or  more  in  thickness. 
Provided,  //<wrrrr,  That  lining  of  steam  chimney,  between  24 
inches  and  32  inches  diameter  and  9/3  inch  thick,  and  lining  be- 
tween 32  and  46  inches  diameter,  11-16  inch  thick,  may  be  used 
in  lengths  not  exceeding  8  feet,  without  bracing. 

The  pressure  of  steam  to  be  allowed  on  linings  shall  be 
determined  by  the  following  formula,  viz  : 
Constant,  89600. 
D  =  diameter  in  inches. 
T  =  thickness  in  decimals  of  an  inch. 
L  —  length  in  feet. 
P  =  pressure  of  steam  allowable  in  pounds. 

89600  X  T2 

Formula   :  —  T        ^  —  =  P. 
i^  x  D 

And  the  length  of  the  lining  or  flue  shall  be  the  distance 
between  center  and  center  of  angle  rings,  or  center  of  angle 
rings  to  center  of  nearest  row  of  rivets  holding  head,  but  in  no 
case  shall  this  distance  be  greater  than  2.]/2  feet,  except  as  other- 
wise provided. 

Corrugated  or  ribbed  flues  may  be  used  as  lining  to  steam 
chimney  or  superheaters  under  the  same  rules  and  conditions 
as  apply  to  their  use  in  the  furnaces  of  steam  boilers. 

Crown  Bars. 
Working  pressure  =         Ip    X*D  x  L 


Where  W  =  Width  of  combustion  box  in  inches. 
P  =  Pitch  of  supporting  bolts  in  inches. 
D  =  Distance  between  girders  from  center  to  cen- 

ter in  inches. 
L  =  Length  of  girder  in  feet. 


i46  PRACTICAL  MARINE  ENGINEERING. 

d  =  Depth  of  girder  in  inches. 

T  =  Thickness  of  girder  in  inches. 

C  —  550  when  the  girder  is  fitted  with  one  sup- 
porting bolt. 

C  =  825  when  the  girder  is  fitted  with  two  or  three 

supporting  bolts. 

C  =  935  when  the  girder  is  fitted  with  four  sup- 
porting bolts. 

Boiler  Heads  (Special  Class). 

All  heads  employed  in  the  construction  of  cylindrical  boilers 
for  steamers  navigating  the  Red  River  of  the  North,  and  rivers 
whose  waters  flow  into  the  Gulf  of  Mexico,  shall  have  a  thick- 
ness of  material  as  follows :  For  boilers  having  a  diameter  ex- 
ceeding 32  inches  and  not  exceeding  36  inches,  not  less  than 
half  an  inch;  for  boilers  exceeding  36  inches  in  diameter  and 
not  exceeding  40  inches  in  diameter,  not  less  than  nine-six- 
teenths of  an  inch ;  for  boilers  exceeding  40  inches  in  diameter, 
not  less  than  one-sixteenth  of  an  inch  additional  thickness  for 
every  8  inches  additional  diameter,  required  for  boilers  40 
inches  in  diameter. 

And  the  heads  of  steam  and  mud  drums  of  such  boilers  shall 
have  a  thickness  of  material  not  less  than  half  an  inch. 

Bumped  heads  may  have  a  manhole  opening  flanged  in- 
wardly, when  such  flange  has  sufficient  depth  and  thickness  to 
furnish  as  many  cubic  inches  of  material  as  was  removed  from 
the  head  to  form  such  opening. 

Bumped  Heads  of  Boilers. 

Multiply  the  thickness  of  the  plate  by  one-sixth  of  the  ten- 
sile strength,  and  divide  by  one-half  of  the  radius  to  which  head 
is  bumped,  which  will  give  the  pressure  per  square  inch  of  steam 
allowed. 

To  find  the  radius  of  sphere  of  which  the  bumped  head 
forms  a  part,  square  the  radius  of  the  head.  Divide  this  by  the 
height  of  bump  required.  To  this  result  add  height  of  bump. 
This  will  give  diameter  of  sphere,  one-half  of  which  will  be  the 
radius  required. 

Unstayed  Plat  Heads. 

The  pressure  on  unstayed  flat-heads,  when  made  of  stamped 
material,  on  steam  drums  or  shells  of  boilers,  when  flanged  and 


BOILERS.  147 

made  of  wrought  iron  or  steel  or  of  cast  steel,  shall  be  deter- 
mined by  the  following  rule : 

The  thickness  of  plate  in  inches  multiplied  by  one-sixth  of 
its  tensile  strength  in  pounds,  which  product  divided  by  the  area 
of  the  head  in  square  inches  multiplied  by  .09  will  give  pressure 
per  square  inch  allowed.  The  material  used  in  the  construction 
of  flat-heads  when  tensile  strength  has  not  been  officially  de- 
termined shall  be  deemed  to  have  a  tensile  strength  of  45,000 
pounds. 

When  such  heads  are  stayed  or  braced,  the  pressure  al- 
lowed shall  be  determined  as  above  for  flat  surfaces. 

Pressure  Allowable  for  Concaved  Heads  of  Boilers. 

Multiply  the  pressure  per  square  inch  allowable  for  bumped 
heads  attached  to  boilers  or  drums  convexly,  by  the  constant  .6, 
and  the  product  will  give  the  pressure  per  square  inch  allowable 
in  concaved  heads. 

Manholes. 

All  manholes  for  the  shell  of  boilers  over  40  inches  in  di- 
ameter shall  haye  an  opening  not  less  than  n  by  15  inches  in 
the  clear,  except  that  boilers  40  inches  diameter  of  shell  and 
under  shall  have  an  opening  of  not  less  than  9  by  15  inches  in 
the  clear  in  manholes. 

When  holes  exceeding  6  inches  in  diameter  are  cut  in  the 
boilers  for  pipe  connections,  man  and  hand  hole  plates,  such 
holes  should  be  reinforced,  either  on  the  inside  or  outside  of 
boiler,  with  reinforcing  plates,  which  shall  be  securely  riveted 
to  the  boiler,  *  *  *  *  *  such  reinforcing  material  to  be 
of  wrought  iron  or  steel  rings  of  sufficient  width  and  thickness 
of  material  to  equal  the  amount  of  material  cut  from  such 
boilers,  in  flat  surfaces ;  and  where  such  opening  is  made  in  the 
circumferential  plates  of  such  boilers,  the  reinforcing  ring  shall 
have  a  sectional  area  of  at  least  one-half  the  area  of  material 
there  would  be  in  a  line  drawn  across  such  opening  parallel  with 
the  longitudinal  seams  of  such  portion  of  the  boiler.  On  boilers 
carrying  75  pounds  or  less  steam  pressure  a  cast  iron  stop  valve, 
properly  flanged,  may  be  used  as  a  reinforce  to  such  opening. 
When  holes  are  cut  in  any  flat  surface  of  such  boilers,  and  such 
holes  are  flanged  inwardly  to  the  depth  of  not  less  than  il/> 
inches,  measuring  from  the  outer  surface,  the  reinforcement 
rings  may  be  dispensed  with. 


148  PRACTICAL  MARINE  ENGINEERING. 

Also  plates  constructed  of  plate  steel  of  corrugated  form, 
without  opening  in  plate  for  bolt,  corrugation  forming  support 
for  bolt,  will  be  allowed  for  use  for  manhole  and  hand-hole 
openings. 

No  connection  between  shell  of  boiler  and  mud  drum  ex- 
ceeding 6  inches  in  diameter  will  be  allowed. 

Safety  Plugs. 

All  steamers  shall  have  inserted  in  their  boilers  plugs  of 
Banca  tin,  at  least  one-half  inch  in  diameter  at  the  smallest  end 
of  the  internal  opening,  in  the  following  manner,  to  wit :  Cyl- 
inder boilers  with  flues  shall  have  one  plug  inserted  in  one  flue 
of  each  boiler;  and  also  one  plug  inserted  in  the  shell  of  each 
boiler  from  the  inside,  immediately  below  the  fire  line,  and  not 
less  than  4  feet  from  the  forward  end  of  the  boiler.  All  fire-box 
boilers  shall  have  one  plug  inserted  in  the  crown  of  the  back 
connection  or  in  the  highest  fire  service  of  the  boiler.  All  up- 
right tubular  boilers  used  for  marine  purposes  shall  have  a 
fusible  plug  inserted  in  one  of  the  tubes  at  a  point  at  least  2 
inches  below  the  lower  gauge  cock,  and  said  plug  may  be  placed 
in  the  upper  head  sheet  when  deemed  advisable  by  the  local  in- 
spectors. All  fusible  plugs,  unless  otherwise  provided,  shall 
have  an  external  diameter  not  less  than  that  of  a  i  inch  gas  or 
steam  pipe  screw  tap,  except  when  such  plugs  shall  be  used  in 
the  tubes  of  upright  boilers,  plugs  may  be  used  with  an  external 
diameter  of  not  less  than  that  of  a  three-eighths  of  an  inch  gas 
or  steam  pipe  screw  tap,  said  plugs  to  conform  in  construction 
with  plugs  now  authorized  to  be  used  by  this  Board ;  and  it 
shall  be  the  duty  of  the  inspectors  to  see  that  these  plugs  are- 
filled  with  Banca  tin  at  each  annual  inspection. 

Gauge  Cocks. 

All  steamers  having  one  or  two  boilers  shall  have  three 
suitable  gauge  cocks  in  each  boiler.  Those  having  three  or 
more  boilers  in  battery  shall  have  three  in  each  outside  boiler 
and  two  in  each  remaining  boiler  in  the  battery ;  and  the  middle 
gauge  cocks  in  all  boilers  shall  not  be  less  than  4  inches  above 
the  top  of  the  flues,  tubes,  or  crown  of  the  fire  box. 

Safety  Valves. 

Lever  safety  valves  to  be  attached  to  marine  boilers  shall 
have  an  area  of  not  less  than  I  square  inch  to  2  square  feet  of 


BOILERS.  149 

the  grate  surface  in  the  boiler,  and  the  seats  of  all  such  safety 
valves  shall  have  an  angle  of  inclination  of  45  degrees  to  the 
center  line  of  their  axis. 

The  valves  shall  be  so  arranged  that  each  boiler  shall  have 
one  separate  safety  valve,  unless  the  arrangement  is  such  as  to 
preclude  the  possibility  of  shutting  off  the  communication  of  any 
boiler  with  the  safety  valve  or  valves  employed.  This  arrange- 
ment shall  also  apply  to  lock-up  safety  valves  when  they  are  em- 
ployed. 

Any  spring-loaded  safety  valves  constructed  so  as  to  give 
an  increased  lift  by  the  operation  of  steam,  after  being  raised 
from  their  seats,  or  any  spring-loaded  safety  valve  constructed 
in  any  other  manner  so  as  to  give  an  effective  area  equal  to  that 
of  the  aforementioned  spring-loaded  safety  valve,  may  be  used 
in  lieu  of  the  common  lever-weighted  valve  on  all  boilers  on 
steam  vessels,  and  all  such  spring-loaded  safety  valves  shall  be 
required  to  have  an  area  of  not  less  than  I  square  inch  to  3 
square  feet  of  grate  surface  of  the  boiler,  except  as  hereinafter 
otherwise  provided  for  water-tube  or  coil  and  sectional  boilers, 
and  each  spring-loaded  valve  shall  be  supplied  with  a  lever  that 
will  raise  the  valve  from  its  seat  a  distance  of  not  less  than  that 
equal  to  one-eighth  the  diameter  of  the  valve  opening,  and  the 
seats  of  all  such  safety  valves  shall  have  an  angle  of  inclination 
to  the  center  line  of  their  axis  of  45  degrees.  All  spring-loaded 
safety  valves  for  water-tube  or  coil  and  sectional  boilers  re- 
quired to  carry  a  steam  pressure  exceeding  175  pounds  per 
square  inch  shall  be  required  to  have  an  area  of  not  less  than  I 
square  inch  to  6  square  feet  of  the  grate  surface  of  the  boiler. 
Nothing  herein  shall  be  construed  to  prohibit  the  use  of  two 
safety  valves  on  any  water-tube  or  coil  and  sectional  boiler,  pro- 
vided the  combined  area  of  such  valves  is  equal  to  that  required 
by  rule  for  one  such  valve.  But  in  no  case  sha'll  any  spring- 
loaded  safety  valve  be  used  in  lieu  of  the  lever-weighted  safety 
valve  without  first  having  been  approved  by  the  Board  of  Su- 
pervising Inspectors. 

The  first  paragraph  of  this  section  applies  to  valves  con- 
structed in  material,  workmanship,  and  principle  according  to 
the  drawings  for  a  safety  valve  printed  with  these  rules,  and  all 
common  lever  safety  valves  to  be  hereafter  applied  to  the  boilers 
of  steam  vessels  must  be  so  constructed. 


i5o  PRACTICAL  MARINE  ENGINEERING. 

Copper  Steam  Pipe. 

All  copper  steam  pipes  shall  be  flanged  to  a  depth  of  not 
less  than  four  times  the  thickness  of  the  material  in  the  pipes, 
and  all  such  flanging  shall  be  made  to  a  radius  not  to  exceed  the 
thickness  of  the  material  in  such  pipes.  And  all  such  pipes  shall 
have  a  thickness  of  material  according  to  the  working  steam, 
pressure  allowed,  and  such  thickness  of  material  shall  be  de- 
termined by  the  following  rule : 

Rule. — Multiply  the  working  steam  pressure  in  pounds  per 
square  inch  allowed  the  boiler  by  the  diameter  of  the  pipe  in 
inches,  then  divide  the  product  by  the  constant  whole  number 
8000,  and  add  .0625  to  the  quotient ;  the  sum  will  give  the  thick- 
ness of  material  required. 

The  flanges  of  all  copper  steam  pipes  over  3  inches  in  di- 
ameter shall  be  made  of  bronze  or  brass  composition,  shall  be 
securely  brazed  to  pipe,  and  shall  have  a  thickness  of  material 
of  not  less  than  four  times  the  thickness  of  material  in  the  pipes 
plus  .25  of  an  inch;  and  all  such  flanges  shall  have  a  boss  of 
sufficient  thickness  of  material  projecting  from  the  back  of  the 
flange  a  distance  sufficient  to  be  properly  riveted  to  the  pipe, 
and  of  a  thickness  of  not  less  than  one-half  inch ;  and  all  such 
flanges  shall  be  counterbored  in  the  face  to  fit  the  flange  of  the 
pipe;  and  the  joints  of  all  copper  steam  pipes  shall  be  made 
with  a  sufficient  number  of  good  and  substantial  bolts  to  make 
such  joints  at  least  equal  in  strength  to  all  other  parts  of  the 
pipe. 

Steel  and  Iron  Pipe. 

The  terminal  and  intermediate  joints  of  all  wrought  iron 
and  homogeneous  steel  feed  and  steam  pipes  over  3  inches  in 
diameter,  other  than  on  pipe  or  coil  boilers  or  steam  generators, 
shall  be  made  of  wrought  iron,  homogeneous  steel,  or  flanges 
of  equivalent  material ;  and  all  such  flanges  shall  have  a  depth 
through  the  bore  of  not  less  than  that  equal  to  one-half  of  the 
diameter  of  the  pipe  to  which  any  such  flange  may  be  attached ; 
and  such  bores  shall  taper  slightly  outwardly  toward  the  face  of 
the  flanges ;  and  the  ends  of  such  pipes  shall  be  enlarged  to  fit 
the  bore  of  the  flanges,  and  they  shall  be  substantially  beaded 
into  a  recess  in  the  face  of  each  flange. 

But  where  such  pipes  are  made  of  extra  heavy  lap-welded 
steam  pipe  up  to  and  including  5  inches  the  flanges  may  be  at- 


BOILERS.  151 

tached  with  screw  threads  ;  and  all  joints  in  bends  may  be  made 
with  good  and  substantial  malleable  iron  elbows  or  equivalent 
material. 

All  feed  and  steam  pipes  not  over  2  inches  in  diameter  may 
be  attached  at  their  terminal  and  intermediate  joints  with  screw 
threads  by  flanges,  sleeves,  elbows,  or  union  couplings ;  but 
where  the  ends  of  such  pipes  at  their  terminal  joints  are  screwed 
into  material  in  the  boiler,  drum,  or  other  connection  having  a 
thickness  of  not  less  than  y2  inch,  the  flanges  at  such  terminal 
joints  may  be  dispensed  with.  Where  any  such  pipes  are  not 
over  i  inch  in  diameter  and  any  of  the  terminal  ends  are  to  be 
attached  to  material  in  the  boiler  or  connection  having  a  thick- 
ness of  less  than  y2  inch,  a  nipple  shall  be  firmly  screwed  into 
the  boiler  or  connection  against  a  shoulder,  and  such  pipe  shall 
be  screwed  firmly  into  such  nipple.  And  should  inspectors 
deem  it  necessary  for  safety  they  may  require  a  jam  nut  to  be 
screwed  onto  the  inner  end  of  any  such  nipple. 

The  word  "terminal"  shall  be  interpreted  to  mean  the  points 
where  steam  or  feed  pipes  are  attached  to  such  appliances  on 
boilers,  generators,  or  engine,  as  are  placed  on  such  to  receive 
them. 

All  lap-welded  iron  or  steel  steam  pipes  over  5  inches  in 
diameter  or  riveted  wrought  iron  or  steel  steam  pipes  over  5 
inches  in  diameter,  in  addition  to  being  expanded  into  tapered 
holes  and  substantially  beaded  into  recess  in  face  of  flanges, 
shall  be  substantially  and  firmly  riveted  with  good  and  sub- 
stantial rivets  through  the  hubs  of  such  flanges,  and  no  such 
hubs  shall  project  from  such  flanges  less  than  2  inches  in  any 
case. 

No  cast  iron  nozzles,  branch  pipes,  or  elbows  shall  be  used 
in  connecting  steam  drums,  superheaters,  branch  pipes,  or 
steam  pipes  to  boilers,  and  in  no  other  part  of  steam  pipes. 
Flanges  welded  to  wrought  iron,  Bessemer,  or  other  steel  pipe 
may  be  used.  No  cast  iron  flanges  will  be  allowed  to  be  used 
on  boilers  for  marine  purposes  unless  such  cast  iron  has  been 
officially  tested  and  test  on  record  in  the  office  of  the  local  in- 
spectors where  boiler  with  such  appliances  was  constructed, 
and  no  cast  iron  with  a  tensile  strength  of  less  than  30,000 
pounds  will  be  permitted  to  be  used  for  such  purposes.  Semi- 
steel  of  not  less  than  24,000  pounds  tensile  strength  may  be  used 
for  nozzles,  stop-valves,  branch  pipes,  elbows,  slip-joints,  flanges 


i52  PRACTICAL  MARINE  ENGINEERING. 

to  boilers,  tee  pipes,  and  water  and  gauge  cock  pipes  or  columns, 
when  said  semi-steel  has  been  officially  tested,  and  test  on 
record  in  the  office  of  the  local  inspectors,  same  as  is  required 
of  cast  iron. 

Coil  and  Ttibulous  Boilers. 

All  coil  and  pipe  boilers  hereafter  made,  when  such  boiler  is 
completed  and  ready  for  inspection,  must  be  subjected  at  in- 
spection to  a  hydrostatic  pressure  double  that  of  the  steam 
pressure  allowed  in  the  certificate  of  inspection — to  take  effect 
on  and  after  July  I,  1897. 

The  use  of  cast-steel  manifolds,  tees,  return  bends,  or  el- 
bows in  the  construction  of  pipe  generators  shall  be  allowed, 
and  the  pressure  of  steam  shall  not  be  restricted  to  less  than 
one-half  the  hydrostatic  pressure  applied  to  pipe  generators, 
unless  a  weakness  should  develop  under  such  test  as  would  ren- 
der it  unsafe  in  the  judgment  of  the  inspector  making  such 
inspection. 

All  drums  attached  to  coil,  pipe,  sectional,  or  water-tube 
boilers  not  already  in  use  or  actually  contracted  for,  to  be  built 
for  use  on  a  steam  vessel,  and  its  building  commenced  at  or 
before  the  date  of  the  approval  of  this  rule,  shall  be  required  to 
have  the  heads  of  wrought  iron  or  steel  or  cast  steel,  flanged 
and  substantially  riveted  to  the  drums,  or  secured  by  bolts  and 
nuts  of  equal  strength  with  rivets,  in  all  cases  where  the  di- 
ameters of  such  drums  exceed  6  inches. 

Except  steam  drums  not  exceeding  15  inches  diameter  at- 
tached to  coils  or  pipe  generators  may  be  used  when  heads  are 
made  of  malleable  iron  or  cast  steel,  said  drums  being  threaded 
on  outside  of  such  shell  with  a  good  full  U.  S.  standard  thread, 
eight  to  the  inch,  for  a  distance  of  at  least  I  inch  on  such  shell, 
the  thread  on  head  to  correspond  with  the  same  and  well  fitted ; 
the  end  of  shell  projecting  beyond  the  threaded  part  and  screwed 
against  a  packing  that  will  prevent  water  or  steam  to  come  in 
contact  with  the  threaded  part : 

PROVIDED,  Such  steam  drums  are  placed  outside  of  and  not 
brought  in  contact  with  the  heat  or  gases  used  in  generating 
steam,  and  have  been  subjected  to  a  hydrostatic  pressure  of 
double  the  steam  pressure  allowed. 

Drums  and  water  cylinders  constructed  with  bumped  head 
at  each  or  either  end,  any  opening  in  the  shell  or  heads  to  be  re- 
inforced as  required  by  the  rules  of  the  Board,  the  circumfer- 


BOILERS.  153 

ential  and  horizontal  seams  to  be  welded  and  properly  annealed 
after  such  welding  is  completed,  and  when  tested  with  a  hy- 
drostatic pressure  of  at  least  double  the  amount  of  steam  pres- 
sure allowed,  may  be  used  for  marine  purposes. 


154  PRACTICAL  MARINE  ENGINEERING. 


CHAPTER   IV. 

MARINE  ENGINES. 

Sec.  20.    TYPES  OF  ENGINES  AND  ARRANGEMENT  OF 

PARTS. 

The  various  types  of  marine  steam  engine  may  be  classi- 
fied in  different  ways,  according  to  the  particular  feature  under 
special  consideration.  A  typical  modern  marine  engine  as  in 
Fig.  98  may  be  defined  as  a  vertical,  inverted,  direct-acting, 
multiple-expansion,  condensing,  engine.  Let  us  first  examine  the 
significance  of  these  various  terms. 

In  the  early  days  of  marine  engineering  the  engines  were 
often  horizontal,  as  shown  in  Figs.  101,  102,  and  such  are  still 
met  with  occasionally  in  special  types  of  warship  practice  and 
elsewhere.  An  intermediate  type,  as  shown  in  Fig.  103  and 
known  as  the  inclined  or  diagonal  engine,  has  been  used  to  a 
considerable  extent  with  paddle  wheels.  In  modern  practice, 
with  rare  exceptions,  the  marine  screw  engine  is  vertical,  as  in 
Figs.  97-100. 

In  the  earlier  vertical  marine  engines  the  cylinder  was  at 
the  bottom  and  the  motion  of  the  parts  proceeded  upward 
either  directly  to  the  crank  shaft,  as  in  the  oscillating  engine, 
Fig.  104,  or  to  a  beam  or  intermediate  mechanism,  Fig.  105,. 
whence  it  came  back  to  the  shaft.  In  the  modern  engine  the 
cylinders  are  on  top  and  the  motion  of  the  parts  proceeds  down- 
ward to  the  shaft.  Hence  in  comparison  with  the  earlier  types 
the  modern  engine  is  called  inverted. 

Where  the  connecting-rod  and  crank  lie  beyond  the  cross 
head  or  farther  end  of  the  piston-rod,  as  in  Figs.  97-101,  the 
engine  is  said  to  be  direct-acting.  In  certain  early  types  of  hori- 
zontal engines  in  single  screw  ships,  as  represented  in  Fig.  102, 
the  cylinder  was  sometimes  placed  close  to  the  shaft  and  two 
piston-rods  were  fitted  passing  beyond  the  shaft,  one  above  and 
the  other  below.  Then  from  a  crosshead  at  this  point  the  mo- 


MARINE  ENGINES. 


155 


tion  came  back  to  the  crank  pin  by  a  connecting-rod  in  the 
usual  way.  Such  engines  were  called  return  connecting-rod  or 
back-acting.  In  still  earlier  times  the  same  type  of  engine  placed 
on  end,  with  the  cylinder  at  the  bottom,  and  known  as  the  stee- 


Fig.  97.    Longitudinal  Section,  Compound  Engine,  Mercantile  Type. 

pie  engine,  was  frequently  fitted  in  side-wheel  paddle  steamers, 
and  a  modification  of  this  is  occasionally  met  with  abroad  at 
the  present  time. 

In  early  marine  engines  the  expansion  of  steam  always 


156 


PRACTICAL  MARINE  ENGINEERING. 


MARINE  ENGINES. 


157 


took  place  in  one  cylinder  only.  In  the  typical  modern  engine 
the  steam  is  passed  through  a  series  of  cylinders  from  one  to 
another  of  increasing  size.  Such  engines  in  general  are  termed 


Marine  Engineering 

Fig.  99.    Triple  Expansion  Engine,  End  View  Looking  Aft. 

multiple  expansion.  If  the  steam  is  thus  used  successively  in 
two  cylinders  or  the  expansion  occurs  in  two  stages,  the  engine 
is  said  to  be  a  compound;  if  in  three  cylinders  or  three  stages,  it 


158 


PRACTICAL  MARINE  ENGINEERING. 


is  a  triple  or  triple  expansion;  if  in  four  cylinders  or  four  stages, 
it  is  a  quadruple  or  quadruple  expansion,  etc. 

Where  the  steam  after  being  used  in  the  cylinder  is  ex- 


Fig.  100.    Triple  Expansion  Engine;   End  View   Showing  Condenser  in 
Back   Fr 


ramng. 


hausted  into  the  air,  the  engine  is  said  to  be  high-pressure  or 
non-condensing.  In  the  typical  modern  engine  the  steam  is  ex- 
hausted to  a  condenser,  thus  giving  the  advantage  of  an  in- 


MARINE  ENGINES. 


159 


Such 


creased  ratio  of  expansion  and  a  decreased  back  pressure, 
engines  are  called  condensing. 

Engines  are  often  given  special  names  according  to  the 
nature  of  the  mechanical  movements  employed.  In  the  usual 
type,  as  we  have  already  seen,  the  motion  is  direct-acting  and 
proceeds  through  piston,  piston-rod,  crosshead,  connecting-rod, 


Fig.  101.    Horizontal    Direct   Acting    Engine,    Outline. 

crank-pin  and  crank-shaft.  In  the  beam  engine,  as  shown  in 
Fig.  105,  the  motion  passes  from  the  piston-rod  to  a  crosshead 
and  then  by  link  or  parallel  motion  to  the  beam.  Thence  from 
the  other  end  of  the  beam  it  passes  by  the  connecting-rod  to 
the  crank-pin  and  crank-shaft.  Such  engines  are  especially 
suited  to  side-wheel  paddle  steamers,  and  for  many  years  were 


Fig.  102.     Horizontal  Back  Acting  Engine,  Outline. 

considered  the  standard  engine  for  use  on  river,  bay  and  lake 
steamers.  In  more  recent  practice,  however,  the  vertical  direct- 
acting  engine  with  screw  propeller  is  to  a  considerable  extent 
displacing  the  beam-engine  with  paddle-wheel,  even  in  its  own 
territory. 

In  the  oscillating  engine,  a  favorite  in  British  practice  for 
side-wheel  paddle  steamers,  the  cylinders  are  located  below  the 


160  PRACTICAL  MARINE  ENGINEERING. 

shaft  and  are  swung  on  trunnions,  as  shown  in  Fig.  104.  The 
piston-rod  is  connected  directly  to  the  crank-pin,  the  piston-rod 
and  connecting-rod  forming  thus  but  one  member.  This  mo- 
tion is  made  possible  by  swinging  the  cylinder  on  trunnions,  as 
may  be  readily  seen  by  the  diagram.  The  trunk  type  of  hori- 
zontal engine,  as  shown  in  outline  in  Fig.  106,  was  often  fitted 
in  former  years  where  economy  of  transverse  or  athwartship 
dimension  was  necessary.  In  this  engine  the  use  of  the  piston- 
rod  was  avoided  by  the  large  trunk,  to  which  the  connecting- 
rod  was  directly  attached,  as  shown. 

The  stern-wheel  western  river  boat  engine,  as  shown  in 
Fig.  155,  is  a  direct-acting  horizontal  engine  connected  to  the 
stern  wheel,  and  provided  with  a  peculiar  type  of  valve  gear. 


Fig.  ]03.    Inclined  Engine,  Outline. 

Further  reference  to  some  peculiar  features  of  this  engine  will 
be  made  in  Section  22. 

The  various  members  of  a  multiple-expansion  marine  en- 
gine may  be  arranged  in  a  great  variety  of  ways  as  regards  the 
location  of  the  cylinders,  the  crank  angles,  and  the  way  in  which 
the  cranks  follow  each  other  around  in  the  revolution.  These 
are  illustrated  in  Figs.  107-110.  Of  the  many  combinations 
which  might  be  made,  only  the  more  important  are  men- 
tioned. Throughout  these  diagrams  the  high-pressure  cylinder 
is  denoted  by  //,  the  low-pressure  cylinder  by  L,  the  interme- 
diate cylinder  of  a  triple-expansion  engine  by  /,  and  the  first 
and  second  intermediates  of  a  quadruple-expansion  by/!,and/2, 
respectively.  Where  the  total  cylinder  volume  is  divided  be- 


MARINE  ENGINES. 


161 


tween  i\vo,  each  of  half  size,  both  of  the  latter  are  given  the 
same  letter.  The  course  of  the  steam  through  the  engine  is  also 
indicated  by  the  arrows.  For  compound  engines  the  usual  ar- 
rangements are  illustrated  in  Fig.  108.  We  may  have  two  or 
three  cylinders  and  one,  two  or  three  cranks.  In  the  latter  case 
the  entire  volume  of  low-pressure  cylinder  is  divided  between 
two  cylinders,  each  of  half  the  total  volume.  The  first  arrange- 
ment with  high-pressure  cylinder  on  top  of  low-pressure  is 
known  as  a  single-crank  tandem  compound,  but  is  rarely  met 


Fig.  104.     Oscillating   Engine,    Outline. 


with  in  marine  practice.  The  other  arrangements  may  be 
placed,  of  course,  with  either  end  forward.  The  various  crank 
angles  are  shown  in  Fig.  107  at  I,  2,  3,  4  and  5,  the  crank 
marked  /  in  No.  5  being  in  this  case  for  one  of  the  L.  P.  cylin- 
ders. With  two  cranks  the  angle  between  may  be  either  90  deg. 
or  180  deg.,  or  slightly  greater  or  less  than  180  deg.,  as  175 
deg.  or  185  deg.  The  90  deg.  angle  is  undoubtedly  the  best  for 
all-around  service.  The  180  deg.  angle  gives  a  better  balance 
to  the  moving  parts  and  admits  of  a  simplification  of  valve  gear. 


162 


PRACTICAL  MARINE  ENGINEERING. 


and  is  sometimes  preferred  for  these  reasons.  There  is,  how- 
ever, a  liability  of  the  engine's  sticking  on  the  center  and  the 
general  readiness  of  handling  is  less  than  with  cranks  at  90  deg. 
To  overcome  this,  angles  of  175  deg.  or  185  deg.,  as  shown  at 
2,  are  sometimes  used,  the  balance  of  moving  parts  in  such  case 
being  substantially  as  good  as  with  an  angle  of  180  deg. 


Fig.  105.     Beam  Engine,   Side  Elevation. 


With  three  cranks  the  angles  are  usually  equal,  and  hence 
120  deg.  each.  Occasionally  they  are  slightly  varied  from  these 
values  in  order  to  give  a  more  uniform  rotative  effort,  or  to  give 
a  better  balance  to  the  forces  causing  vibration. 


MARINE  ENGINES. 


163 


For  the  triple-expansion  engine  the  more  important  ar- 
rangements of  cylinders  are  shown  in  Fig.  109.  We  may  have 
three  cylinders  or  more,  and  two,  three  or  more  cranks.  The 


Fig.  106.    Trunk  Engine,   Outline. 

most  common  types  have  either  three  or  four  cranks,  in  the  lat- 
ter case  the  total  L.  P.  volume  being  divided  between  two  cylin- 

(DCDG'OO 


8  9  10  11 

Fig.  107.     Various    Crank    Angles. 


ders,   each   of  half  the   total  volume.     The   crank   angles   are 
usually    1 20   deg.   with   three   cranks,   and  90  deg.   with   four, 


;  * 

•\ 

/             ^^ 

1 

# 

L 

H 

/ 

^ 

L 

L 

H 

L 

7 

2 

/ 

/ 

Fig.  108.     Cylinder  Arrangements  for  Compound  Engine. 

though  occasionally  slight  variations  from  these  values  are 
adopted  in  order  to  obtain  a  better  balance  of  the  forces  causing 
vibration.  Of  the  various  arrangements  of  cylinders  shown  in 


i64 


PRACTICAL  MARINE  ENGINEERING. 


Fig.  109,  each  may,  of  course,  be  placed  either  end  forward  in 
the  ship.  We  may  also  have  the  various  sequences  and  arrange- 
ments of  cranks  as  indicated  in  Fig.  107,  the  changes  of  letter- 
ing where  necessary  being  readily  seen. 

For  the  quadruple-expansion  engine  the  more  important 
cylinder  arrangements  are  shown  in  Fig.  no.     The  number  of 


^_I 

I 

L 

I 

/ 

1 

L 

L 

T 

x  /h 

Fig.  109.     Cylinder   Arrangements    for   Compound    Engine. 


I 

L 

z 

I 

/ 

/ 

3 

/ 


Fig.  110.     Cylinder  Arrangements  for  Quadruple  Expansion  Engine. 

cylinders  may  be  four,  five  or  six,  with  four  or  five  cranks.  With 
five  cranks  the  angles  are  usually  equal,  and  hence  of  72  deg.,. 
though  as  with  three  and  four  cranks  slight  departures  might  be 
made  to  obtain  a  better  balance  of  the  forces  producing  vibra- 
tion. The  arrangements  of  cylinders  shown  in  Fig.  no  may 
l>e  placed  in  the  ship  either  end  forward,  and  various  crank  se- 


MARINE  ENGINES.  165 

qucnccs  in  addition  to  those  shown  in  Fig.  107  may  be  easily 
arranged.  One  of  the  chief  tendencies  of  modern  practice  is  to 
pay  especial  attention  to  the  balancing  of  the  forces  producing 
vibration.  The  use  of  irregular  crank  angles  in  this  connection 
lias  been  already  referred  to.  In  addition,  and  of  not  less  im- 
portance, the  larger  cylinders  with  the  larger  and  heavier  pis- 
tons are  now  frequently  placed  inside,  with  the  lighter  moving 
parts  on  the  outside,  as  in  Fig.  109,  Nos.  3  and  5,  or  Fig. 
no,  No.  2. 

Sec.  21.    DESCRIPTION  OF  PRINCIPAL  PARTS  OF  A 
MARINE  ENGINE. 

In  describing  the  principal  parts  of  the  typical  modern 
marine  engine,  we  may  take  first  the  stationary,  and  then  the 
moving  parts.  [x]  Cylinders. 

As  shown  in  Figs.  97-100,  the  cylinders  are  at  the  top  of  the 
engine  and  consist  each  of  a  cylindrical  chamber  containing  the 
moving  piston.  The  steam  is  received  from  the  steam  chest 
alternately  in  either  end  and  thus  forces  the  piston  up  and  down. 
The  motion  is  then  transmitted  through  the  piston-rod  and  con- 
necting-rod and  thus  the  revolution  of  the  crank  and  the  crank- 
shaft is  produced. 

Cylinders  are  made  of  cast  iron  of  the  highest  grade.  Each 
one,  as  shown  in  the  figures,  consists  essentially  of  a  cylindrical 
body  or  barrel,  with  which  is  usually  cast  the  lower  or  bottom 
head.  With  the  barrel  are  usually  cast  also  the  valve  casings 
and  chests  and  all  ports  and  passages,  as  well  as  the  necessary 
feet  for  attachment  to  the  columns,  lugs  for  attaching  braces, 
etc.  The  top  head  or  cover  is  cast  separately  and  is  secured  to 
an  appropriate  flange  on  the  barrel  by  means  of  stud-bolts.  In 
some  cases  the  head  is  made  in  a  single  thickness,  conical  in 
form  to  correspond  to  the  piston,  and  ribbed  on  top  for 
strength.  In  other  cases  it  is  made  by  a  double  shell  or  in  two 
thicknesses  with  connecting  ribs  between.  The  lower  head  is 
formed  in  the  same  general  way,  but,  as  noted  above,  is  usually 
cast  in  one  piece  with  the  barrel. 

In  many  cylinders,  as  shown  in  Fig.  in,  liners  are  fitted 
within  the  barrel  or  cylinder  proper.  These  are  of  extra  hard 
and  fine  grained  iron,  and  are  fitted  for  one  or  both  of  the  fol- 
lowing purposes:  (i)  To  provide  a  working  surface  admitting 
of  replacement  in  case  of  excessive  wear.  (2)  To  provide  a 


i66 


PRACTICAL  MARINE  ENGINEERING. 


jacket  space  between  the  barrel  and  liner  in  case  the  cylinders 
are  to  have  steam  jackets.  The  space  thus  formed  is  filled  with 
steam  from  the  boiler,  thus  providing  a  jacket  or  layer  of  steam 
entirely  surrounding  the  steam  cylinder.  Such  an  arrangement 
is  known  as  a  steam  jacket,  and  is  used  to  increase  the  economy 
of  the  engine  as  noted  in  Section  59.  The  liners  are  usually 
secured  at  the  lower  end  by  a  flange,  as  shown  in  Figs,  in,  113, 


Marine  'Engineering 

Fig.  111.     Cylinder  with   Liner  and   Double  Valve    Chests. 

the  joint  between  the  end  faces  of  the  liner  and  barrel  being 
carefully  made  in  order  to  prevent  leakage,  especially  if  the 
space  between  the  barrel  and  liner  is  to  be  used  as  a  steam 
jacket.  At  the  upper  end  the  joint  between  liner  and  barrel 
may  be  made  in  a  variety  of  ways. 

As  shown  in  Fig.  112,  a  packing  space  is  formed  between 
the  liner  and  barrel.     This  is  filled  with  some  form  of  elastic 


MARINE  ENGINES. 


167 


packing  held  in  place  by  a  ring  attached  to  the  liner  as  shown. 
In  this  way  the  tipper  end  of  the  liner  is  free  to  come  and  go  as 
expansion  and  contraction  may  require,  while  the  packing  main- 
tains the  joint  steam  tight.  In  another  mode  of  fitting,  a  groove 
of  dovetailed  cross  section  is  turned  out  partly  in  the  liner  and 
partly  in  the  barrel,  and  a  ring  of  soft  metal  or  packing  is  ex- 
panded into  the  space  thus  formed. 

The  bore  of  the  cylinder  or  liner  is  made  uniform  except 
near  the  top  and  bottom,  where  it  is  counterbored  out  slightly 
larger,  so  that  at  the  extreme  ends  of  the  stroke  the  piston 
rings  may  overrun  the  counterbore,  and  thus  avoid  wearing  a 
shoulder  in  the  metal. 


Fig;  112.     Joint   Between   Liner 
and  Barrel,  Top. 


Fig.  113.    Joint  Between  Liner  and 
Barrel,  Bottom. 


Cylinders  as  well  as  steam  jackets  are  usually  provided  with 
drain  cocks  and  valves  with  suitable  piping,  so  that  water  collect- 
ing within  them  may  be  drained  away  In  addition,  automatic 
relief  cocks  or  valves  (see  Sec.  24)  should  be  fitted,  set  to  open 
under  an  appropriate  pressure,  and  thus  furnishing  relief  in  case 
a  large  quantity  of  water  may  find  its  way  into  the  cylinder. 

The  cylinders  are  supported  directly  upon  the  columns 
which  are  attached  to  facings  on  the  lower  head,  or  to  lugs  cast 
on  the  lower  part  of  the  barrel  in  case  its  diameter  is  not  suffi- 
cient to  reach  out  over  the  tops  of  the  columns  Sec  Fig.  114. 
For  mutual  support  the  cylinders  are  quite  commonly  tied  to- 


i68 


PRACTICAL  MARINE  ENGINEERING. 


gather  by  braces,  or  flanged  and  bolted  to  each  other.  In  some 
cases,  however,  the  cylinders  are  allowed  to  stand  alone  and  in- 
dependently, while  in  the  other  cases  of  recent  practice  a  form 
of  connection  has  been  adopted,  consisting  of  a  vertical  tongue 
and  grooved  joint.  This  allows  differences  of  expansion  ver- 
tically and  fore  and  aft,  but  provides  mutual  support  trans- 
versely. 


Fig.  114.   Double    Inverted   Y   Columns. 

The  valve  chests  with  the  various  ports,  passages,  etc.,  are 
also  cast  with  the  cylinders,  as  shown  in  the  figures.  These 
parts  will  receive  further  notice  in  connection  with  valves.  See 
Sec-  46.  [a]  columns. 

The  columns  serve  to  support  the  cylinders  and  to  connect 
them  with  the  bed-plate.  They  also  serve  to  support  the  guide 
surfaces  for  the  crossheads,  and  thus  receive  the  transverse 


MARINE  ENGINES. 


169 


thrust  of  the  connecting-rods.  Columns  are  made  either  of 
cast  iron,  cast  steel  or  forged  steel.  When  of  cast  metal  they 
are  usually  in  the  form  of  an  inverted  Y,  as  shown  in  Figs.  114, 
115,  and  of  a  box  or  I-formed  section.  When  forged,  the  col- 
umns are  usually  cylindrical  or  slightly  tapering,  and  sometimes 
hollow.  Cast  inverted  Y  columns  both  front  and  back  of  the  en- 
gine, as  shown  in  Fig.  114,  for  many  years  constituted  standard 
practice.  More  recently,  however,  cast  inverted  Y  columns  at 
the  back  of  the  engine  and  cylindrical  forged  columns  in  front, 


Fig.  115.    Inverted    Y    and    Cylindrical    Columns. 

as  in  Figs.  115,  116,  are  commonly  employed  in  representa- 
tive marine  practice.  In  such  case  either  one  or  two  columns 
may  be  fitted  in  front  and  one  in  the  rear.  When  the  columns 
are  all  cylindrical,  it  is  customary  to  provide  four  for  each  cyl- 
inder. Such  columns  are  usually  placed  vertical,  as  in  Fig.  117, 
though  occasionally  they  are  spread  somewhat  at  the  base,  as 
in  Fig.  115. 

In  some  cases  of  modern  practice  four  vertical  columns  of 
T  section  have  been  provided  for  use  with  a  crosshead  as  shown 
in  Fig.  134.  The  columns  stand  in  pairs,  one  forward  and  one 


170 


PRACTICAL  MARINE  ENGINEERING. 


aft,  and  the  wings  of  the  crosshead  carrying  the  slide  surfaces 
work  between  them  on  the  guides  carried  on  their  inner  faces. 
In  some  cases  the  condenser  is  placed  back  of  the  engine 


Fig.  116.    Inverted  Y  and   Cylindrical   Columns,  Warship  Type. 

and  on  the  bed-plate,  as  in  Fig.  100.  In  this  case  the  back  col- 
umns are  either  cast  with  the  condenser  shell  or  consist  of  short 
vertical  columns  standing  on  top  of  the  condenser;  which  thus 
constitutes  a  part  of  the  support  of  the  cylinders  as  shown. 


MARINE  ENGINES. 


171 


To  resist  the  racking  and  cross-breaking  stresses  to  which 
the  columns  may  be  subject,  it  is  necessary,  especially  with  plain 
cylindrical  columns,  to  provide  transverse  and  even  longitudinal 
ties  and  braces.  The  usual  arrangement  of  such  bracing  is 
shown  in  Figs.  115,  116,  117.  It  will  be  noted  in  particular  that 
the  transverse  bracing  between  a  pair  of  columns  as  in  Fig.  117 
unites  them  into  a  single  girder,  thus  providing  vastly  more 
strength  to  resist  lateral  stresses  due  to  rolling  of  the  ship,  etc., 
than  could  be  furnished  by  the  columns  themselves  and  without 
the  assistance  which  the  bracing  is  able  to  provide. 


Fig.  117.     Cylindrical    Columns. 

The  guide  surface  for  a  crosshead  is  fitted  in  various,  ways 
according  to  the  style  of  crosshead,  the  style  of  column  and  type 
of  practice.  The  simplest  arrangement  is  as  shown  in  the  cross- 
section  of  Fig.  118,  in  which  the  guide  surface  is  fitted  directly 
on  the  inner  face  of  the  Y  column.  In  the  arrangement  of  Fig. 
115  the  guide  surface  is  fitted  on  a  separate  slab  of  rather  harder 
and  finer  grained  cast  iron,  and  hence  better  adapted  for  bear- 
ing purposes.  Between  this  slab  and  the  face  of  the  column  a 


172 


PRACTICAL  MARINE  ENGINEERING. 


space  is  left  as  shown,  and  through  this  may  be  circulated  a 
stream  of  water  to  absorb  the  heat  generated  by  the  friction, 
and  thus  to  keep  the  bearing  surface  cool.  With  cylindrical  col- 
umns the  guide  curface  must  be  fitted  as  a  separate  slab  for  each 
crosshead,  and  usually  in  the  manner  shown  in  Fig.  117.  These 
slabs  may  be  of  cast  iron,  steel  or  bronze,  and  are  carried  on 
longitudinal  bars  attached  to  the  columns.  The  form  of  cross- 
section  may  be  either  hollow  for  water  circulation,  or  plain  or 
ribbed  on  the  back  for  strength,  as  the  case  may  require.  A 
common  form  is  that  shown  in  Fig.  117,  thinner  towards  the 


Fig.  118.     Section  of  Cast  Column  Showing  Guide  Surface. 

ends  and  thicker  in  the  middle  as  a  girder,  to  provide  the  neces- 
sary strength  at  this  point. 

For  further  details  of  the  guide  surfaces  which  depend  on 
the  form  of  crosshead  used,  reference  may  be  made  to  [7]. 

[3]  Bed-Plates. 

The  purpose  of  the  bed-plate  is  to  support  the  feet  of  the 
columns,  and  thus  to  carry  the  weight  of  the  cylinders  and  at- 
tachments, to  provide  seatings  and  support  for  the  crank-shaft 
bearings,  and  generally  to  serve  as  the  foundation  piece  upon 


MARINE  ENGINES. 


173 


which  the  engine  rests,  and  through  which  its  weight  and  the 
various  stresses  developed  are  transferred  to  the  structure  of 
the  ship. 

As  usually  formed  it  consists  of  a  series  of  transverse  box 


Fig.  119.     Bedplate  for  T 


Marine  Enginttrlng 


pie  Expansion  Engine  in  one  Casting 


or  I  girders,  one  for  each  crank-shaft  bearing,  these  being  con- 
nected together  by  fore  and  aft  members,  as  shown  in  Figs. 
119,  121. 

Bed-plates   are   usually   made   of   cast   iron   or   cast   steel. 


Fig.  120.     Details  of   Bedplate   in    Fig.   119.     Sections   Showing  Main  Pillow    Block. 

Rarely  bronze  or  special  forms  of  plate  girder  may  be  em- 
ployed. Large  bed-plates  instead  of  being  made  in  one  casting 
are  often  made  in  sections  and  bolted  together.  The  bed-plate 
is  secured  to  the  ship  by  holding  doivn  bolts  passing  through  the 


174 


PRACTICAL  MARINE  ENGINEERING. 


flanges  of  the  plate  and  of  the  specially  strengthened  structure 
of  the  ship  underneath,  known  as  the  engine  seating  or  foun- 
dation. Further  examples  of  bed-plates  may  also  be  noted  in 
Figs.  97-100,  114,  116. 


o   o    o 

o 
o 
lo 


Fig1.  121.     Bedplate   in   Sections.     End   View   of   one   Section. 

[4]  Engine  Seating. 

This  structure  is  a  part  of  the  ship,  and  serves  to  give  the 
final  support  to  the  weight  of  the  engine,  and  to  lead  the  stresses 
due  either  to  its  weight  or  to  its  operation,  into  the  structure  of 
the  ship  as  a  whole.  The  usual  character  of  the  seating  is 
shown  in  Fig.  122.  It  consists  of  a  cellular  construction  formed 


0 

o 

\0 

E 

101 

i 

e 

LONGITUDINAL    SECTION. 


TRANSVERSE   VIEW. 
Fig.  122.    Engine    Seating. 

by  longitudinal  and  transverse  vertical  plates,  stiffened  and  con- 
nected at  the  corners  by  angle  irons,  and  usually  forming  a  con- 
tinuous structure  with  a  part,  at  least,  of  the  regular  internal 
members  of  the  ship  itself. 

We  will  now  turn  to  the  chief  moving  parts  of  the  engine. 


MARINE  ENGINES. 


175 


[5]  Pistons. 

The  piston  is  the  moving  part  of  the  engine  upon  which  the 
steam  directly  acts,  and  which  by  the  steam  pressure  is  driven 
back  and  forth  in  the  cylinder,  and  from  which,  through  the 
piston-rod,  crosshead  and  connecting-rod,  the  motion  is  trans- 


Fig.  123.    Conical   Marine   Piston. 

mitted  to  the  crank  and  crank-shaft.  The  requirements  for  the 
piston  are  therefore :  (i)  It  must  be  able  to  support  the  load 
which  the  steam  pressure  brings  upon  it.  (2)  It  must  be  of  such 
form  as  to  admit  of  movement  up  and  down  in  the  cylinder,  at 
the  same  time  making  a  steam  tight  joint  between  its  outer  edge 


Fig.  124.     Marine   Piston,    Enlarged   View,   Showing   Packing 
Rings  and  Follower    Plate. 

and  the  cylinder  walls.  (3)  Provision  must  be  made  for  its  se- 
cure attachment  to  the  piston-rod,  through  which  the  forces  are 
transmitted  to  the  remaining  moving  parts  of  the  engine. 

The  usual  form  of  marine  piston  is  shown  in  Fig.  123,  and 
consists  of  a  shell  of  conical  form  with  a  central  boss  or  body  for 
carrying  the  piston-rod  as  shown.  Around  the  outer  edge  of 


i76  PRACTICAL  MARINE  ENGINEERING. 

the  piston  the  metal  is  thickened  up  to  provide  for  the  packing- 
rings,  which  are  fitted  to  make  a  steam  tight  joint  between  the 
piston  and  cylinder  walls.  The  fitting  of  these  rings  is  shown  in 
124.  The  rings  are  usually  two  in  number,  and  are  formed 


TOP-RING 


w-J 


Fig.  1.25.    Marine  Piston,  Joint  in  Packing  Rings. 

of  cast  iron  turned  first  to  an  outside  diameter  slightly  larger 
than  the  bore  of  the  cylinder.-  They  are  then  cut  as  shown  in 
Fig.  125,  and  enough  is  taken  out  so  that  they  may  be  sprung 
together  sufficiently  to  allow  their  entrance  into  the  cylinder 
bore.  Care  is  taken  to  so  locate  the  two  rings  that  the  cuts 


Marine  Engineering 

Fig.  126.    Marine  Piston,  Steel  Springs  for  Packing  Rings. 


shall  not  come  opposite,  and  thus  the  opportunity  for  a  direct 
leak  through  from  one  side  to  the  other  is  avoided.  In  order  to 
still  further  prevent  such  leakage,  a  tongue  as  shown  in  the 
figure  is  usually  fitted  across  the  opening.  The  tongue  piece, 
which  is  usually  of  brass,  is  attached  to  the  ring  and  overlaps 


MARINE  ENGINES. 


177 


the  slit,  as  shown.  The  joints  between  the  ring  and  tongue 
piece  are  carefully  fitted  so  that  in  this  way  the  ring  may  open 
and  shut  as  circumstances  may  require,  while  the  opening  into 
the  slit  remains  closed  to  the  entrance  of  steam.  When  the  pis- 
ton is  of  any  considerable  size  it  is  customary  to  aid  the  natural 
elasticity  of  the  rings  by  steel  springs,  as  shown  in  Fig.  126. 
These  bear  on  the  bottom  of  the  recess  formed  in  the  piston, 
and  on  the  inner  surface  of  the  rings,  and  thus  the  latter  are 
forced  outward  against  the  surface  of  the  cylinder. 

The  body  of  the  piston  itself,  as  shown  in  Fig.  124,  is  turned 
slightly  smaller  than  the  diameter  of  the  cylinder,  so  that  it 
clears  the  latter  at  all  times,  while  the  rings  extend  beyond  and 
make  the  joint  with  the  cylinder  wall.  The  rings  and  springs 


Fig.  127.  Ramsbottom  Rings. 

are  fitted  as  shown  between  the  lower  flange  of  the  piston  body 
an-1  a  plate  known  as  the  follower  plate  or  ring.  By  removing 
the  latter  the  rings  and  springs  may  be  removed  when  necessary 
for  overhauling  ana  refitting.  The  follower  plate  is  secured  to 
the  piston  by  stud  bolts  and  nuts,  as  shown  in  the  figure.  In  the 
best  class  of  work  all  joints  between  the  piston  and  rings,  be- 
tween the  follower  plate  and  rings  and  between  the  two  latter 
are  carefully  made  by  hand  scraping  and  fitting,  in  order  to  re- 
duce the  chances  of  leakage  to  the  smallest  possible  limits. 

Many  variations  are  met  with  in  the  details  of  the  form  and 
fittings  of  pistons.  In  some  cases  they  are  flat  and  either  solid 
or  hollow,  as  shown  in  Figs.  97,  128. 


PRACTICAL  MARINE  ENGINEERING. 


In  some  cases  ramsbottom  rings  are  fitted  instead  of  the 
rings  of  Fig.  123.  These  consist  of  two  or  three  narrow  rings 
turned  slightly  larger  than  the  cylinder  with  a  piece  cut  out  so 
that  they  may  be  sprung  on  over  the  body  of  the  piston,  and  into 
grooves,  as  shown  in  Fig.  127.  No  special  springs  are  fitted, 
and  the  natural  elasticity  of  the  rings  is  depended  upon  to  give 
the  necessary  pressure  between  the  ring  surface  and  the 
cylinder. 

It  is  easily  seen  that  no  follower  plates  being  fitted,  the 
rings  cannot  be  examined  or  removed  without  removing  the 
piston.  To  avoid  this  difficulty  the  arrangement  of  Fig.  128  is 
sometimes  used.  Here  the  rings  are  carried  on  a  larger  solid  ring, 
as  shown,  and  sometimes  known  as  a  bull  ring.  This  is  carried 
between  the  faces  of  the  piston  flange  and  follower  plate,  and 
thus  by  the  removal  of  the  latter  the  whole  arrangement  may  be 
withdrawn  and  examined.  There  is  usually  some  clearance  be- 
tween the  inner  surface  of  the  bull  ring  and  the  body  of  the  pis- 


Fig.  128.     Piston  with  Ramsbottom  Rings  on  Bull  Ring. 

ton,  as  shown  in  the  figure.  This  allows  the  whole  arrange- 
ment of  rings  to  move  transversely  independent  of  the  piston 
body,  thus  making  allowance  for  lack  of  alignment  between  the 
axis  of  the-  piston-rod  and  the  axis  of  the  cylinder,  or  for  wear 
in  the  latter. 

While  light  packing  rings  of  cast  iron  fitted  as  above  de- 
scribed without  the  assistance  of  steel  springs  may  prove  satis- 
factory for  small  pistons,  the  more  standard  method  of  Fig.  123 
is  to  be  recommended  for  all  cases  where  the  pistons  are  of  any 
considerable  size. 

In  present  practice  pistons  of  the  form  shown  in  Fig.  123 
are  made  of  cast  steel.  Pistons  of  the  form  shown  in  Figs.  97, 
128,  are  more  commonly  made  of  cast  iron. 

The  chief  advantage  of  the  conical  form  of  piston  lies  in  the 
saving  of  weight  for  the  necessary  strength  and  stiffness,  as 
compared  with  other  forms.  This  superiority  has  gained  for  it 


MARINE  ENGINES. 


179 


almost  universal  adoption  in  modern  practice,  and  it  may  be 
considered  as  the  present  day  representative  form  of  marine 
piston,  and  the  one  which  will  naturally  be  adopted  unless  there 
may  exist  special  reasons  for  the  adoption  of  the  older  type. 

[6]  Piston-Rods. 

The  piston-rod  is  that  member  of  the  moving  parts  which 
serves  to  support  the  piston,  to  carry  the  forces  due  to  the 
steam  pressure  through  the  stuffing  box  outside  the  cylinder, 
and  through  the  crosshead  to  communicate  them  to  the  connect- 
ing-rod and  other  moving  parts.  The  requirements  are  there- 
fore as  follows :  (i)  It  must  have  sufficient  strength  and  stiffness 
to  safely  carry  the  load  coming  from  the  piston.  (2)  It  must 
be  provided  at  the  upper  end  for  attachment  to  the  piston,  and 
at  the  lower  end  to  the  crosshead.  (3)  It  must  be  of  such  form 
as  to  admit  of  readily  making  a  steam  tight  joint  where  it  passes 
out  of  the  cylinder.  To  fulfil  these  conditions  the  piston-rod,  as 


— 

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Marine  Engineering 


Fig.  129.     Piston  Rod. 


shown  in  Fig.  129,  has  the  form  of  a  uniform  cylindrical  rod  ex- 
cept at  the  ends  where  it  joins  the  piston  and  crosshead.  The 
common  form  of  attachment  to  the  piston  is  shown  in  the  figure. 
The  rod  is  sometimes  tapered  where  it  lies  in  the  piston,  and 
sometimes  parallel.  It  is  often  relieved  from  direct  bearing  ex- 
cept near  the  top  and  bottom,  so  as  to  give  definite  points  of 
bearing  where  it  is  most  needed.  A  shoulder  or  ring  is  also 
fitted,  as  shown,  so  as  to  give  a  definite  stop  against  which  the 
Dody  of  the  piston  rests.  The  end  of  the  rod  is  threaded  and  a 
nut  on  top  completes  the  fastening.  This  nut  is  sometimes 
hexagonal  and  sometimes  cylindrical  with  longitudinal  grooves, 
a  spanner  wrench  being  used  in  the  latter  case  to  set  the  nut 
down. 

The  fitting  at  the  lower  end  of  the  piston-rod  depends  on 
the  style  of  crosshead  used,  and  may  be  more  appropriately  de- 
scribed under  that  heading. 

In  modern  practice  with  conditions  requiring  the  highest 
grade  of  material  and  most  careful  design,  the  piston-rod  is 


i8o 


PRACTICAL  MARINE  ENGINEERING. 


often  made  hollow.  This  practice  also  extends  to  most  of  the 
other  cylindrical  elements  of  the  engine  such  as  cylindrical  col- 
umns, crosshead  pins,  connecting-rods,  crank-pins,  crank,  line, 


Fig.  130.     Marine    Crosshead. 


thrust,  and  propeller  shafts.  Inasmuch  as  this  style  of  construc- 
tion was  first  commonly  introduced  in  connection  with  shafting, 
the  reasons  for  such  practice  and  its  advantages  may  properly 
be  discussed  under  that  heading. 


Fig.  131.     Marine    Crosshead,    Slipper    Type    with    Cotter    Fastening    for 
Piston    Rod. 

[7]  Crossheads. 

There  are  several  types  of  crosshead  to  be  met  with  in 
marine  practice.     In  Fig.  130  is  shown  one  of  the  more  com- 


MARINE  ENGINES. 


181 


mon  forms.  It  consists  essentially  of  a  cubical  body  A,  through 
which  in  a  vertical  direction  is  the  hole  for  the  piston-rod.  Ex- 
tending out  on  either  side  longitudinally  are  the  two  crosshead 


VERTICAL  VIEW.  TRANSVERSE   VIEW. 

Fig.  132.     Marine  Crosshead,  Slipper  Type. 


pins  B  and  C.  Then  attached  to  the  two  remaining  sides  trans- 
versely are  the  slides  as  shown.  The  connection  between  the 
crosshead  and  the  piston-rod  is  commonly  by  means  of  thread 
and  nut,  as  shown  in  the  figure,  in  the  -same  way  as  for  the  con- 


Marixt  Engineering 

Fig.  133.     Crosshead   formed   on   Lower  End   of   Piston   Rod. 

nection  to  the  piston.  In  some  cases  a  pin  or  cotter  joint,  as 
shown  in  Fig.  131,  is  used  instead  of  the  thread  and  nut  on  the 
end.  The  slide  surfaces  D  and  E  rest  on  the  guide  surfaces  of 
the  columns,  as  above  described,  one  side  taking  the  load  when 


182 


PRACTICAL  MARINE  ENGINEERING. 


going  ahead  and  the  other  when  backing.  A  crosshead  of  this 
type  is  therefore  suitable  for  double  inverted  Y  columns  where 
there  is  a  guide  surface  on  both  back  and  front  sides  of  the  en- 
gine. Where  cylindrical  columns  are  used,  as  in  Figs.  115-117, 
the  slipper  form  of  crosshead  is  commonly  fitted.  This  is  shown 
in  Fig.  132,  and  so  far  as  the  part  connected  with  the  piston- 
rod  and  carrying  the  crosshead  pins  is  concerned  may  be  the 
same  as  in  Fig.  130.  Instead  of  two  wings  carrying  slides,  how- 
ever, there  is  but  one  with  the  form  shown  in  the  vertical  view. 
The  corresponding  form  of  guide  is  shown  in  Figs.  115,  117. 


Marine  Engineering 


Fig.  134.    Marine  Crosshead,   Special  Type. 


When  going  ahead  the  face  A  of  the  slipper  bears  against  the 
face  B  of  the  guide.  Cheek  pieces  or  gibs  C  and  D  are  se- 
cured to  the  column,  thus  forming  guide  surfaces  on  their  in- 
ner faces  E  and  F.  Against  these  the  faces  G  and  H  of  the  slip- 
per bear  when  in  backing  motion.  The  go-ahead  surface  is 
therefore  formed  on  the  faces  A  and  B  of  the  guide  and  slip- 
per, as  with  Fig.  130,  while  the  backing  surface,  instead  of  be- 
ing provided  on  the  opposite  column  and  on  another  slide  piece 
on  the  other  side  of  the  crosshead,  is  formed  on  the  reverse 
side,  G  and  H,  of  the  slipper,  and  on  the  cheek  pieces,  as  shown. 
These  types  of  crosshead  are  suited  to  the  so-called  forked 
type  of  connecting-rod,  as  described  below,  for  which  the  cross- 


MARINE  ENGINES. 


183 


head  pins  are  a  part  of  or  fast  in  the  crosshead,  and  are  naturally 
two  in  number,  one  on  either  side  fore  and  aft,  as  shown.  In 
the  other  type  of  connecting-rod  which  is  frequently  met  with, 
the  rod  is  not  forked,  and  the  pin  is  fast  in  the  upper  end,  and 
is  single  rather  than  double,  while  the  crosshead  member  fur- 
nishes the  bearing.  This  arrangement  is  shown  in  Fig.  133. 
The  crosshead  body  is  usually  forged  up  on  the  lower  end  of  the 
piston-rod,  and  together  with  a  suitable  cap  and  bearing  brasses 
forms  the  bearing  for  the  pin  which  is  fast  in  the  upper  end  of 
the  connecting-rod,  as  shown.  The  wings  for  carrying  the 
slides  may  be  attached  and  the  slides  may  be  fitted  in  the  same 


d 


Fig.  135.     Marine   Crosshead,   Special   Type. 

general  manner  as  in  Figs.  130,  132,  either  double  or  of  the 
slipper  type. 

A  third  form  of  crosshead  occasionally  found  in  modern 
practice  was  referred  to  in  [2],  and  is  here  shown  in  Fig.  134. 
This  type  of  crosshead  is  a  marine  adaptation  of  a  type  very 
common  in  stationary  engine  practice.  The  slide  surfaces  are 
formed  on  the  opposite  faces  of  webs  or  wings  extending  out 
from  the  body  of  the  crosshead,  and  bearing  on  the  guide  sur- 
faces formed  on  the  columns.  In  Fig.  135  is  shown  a  somewhat 
different  form  of  the  same  type  of  crosshead,  the  latter  being 
suited  to  two  columns  and  the  former  to  four. 

As  noted  in  [6],  the  crosshead-pins,  in  the  most  advanced 
practice,  are  often  made  hollow.  In  some  cases  the  hole  is 


1 84 


PRACTICAL  MARINE  ENGINEERING. 


parallel ;  in  others  its  diameter  decreases  from  the  outer  end 
inward,  thus  giving  the  most  metal  at  the  inner  end,  where  the 
greatest  stresses  are  likely  to  be  found.  See  Fig.  130. 


I 

if 

a 

Marine  Enyineeriny 


Fig.  136.     Marine   Connecting  Rod. 

[8]   Connecting-Rods. 

Fig.  136  illustrates  perhaps  the  more  common  type  of  con- 
necting-rod.   At  the  upper  end  it  is  forked  or  formed  into  a  U 


Fig.  137.     Marine   Connecting   Rod. 

shape,  each  branch  being  provided  with  a  bearing  and  connec- 
tions for  one  of  the  crosshead-pins.  This  type  of  end  corre- 
sponds therefore  to  the  type  of  crosshead  shown  in  Figs. 
130,  132. 


MARINE  ENGINES. 


185 


For  connection  to  the  crank-pin,  the  lower  end  of  the  rod  is 
fitted  with  brasses  and  cap,  all  secured  to  the  forged  out  foot 
of  the  rod  by  through  bolts  as  shown. 

For  the  type  of  crosshead  shown  in  Fig.  133  the  rod  is 
formed,  as  shown  in  Fig.  137,  with  a  U-shaped  upper  end  fitted 
to  receive  the  two  ends  of  the  crosshead-pin,  which  is  thus  made 
fast  to  the  rod.  This  pin  is  then  seated  in  a  bearing  in  the  cress- 
head,  as  described  under  that  heading.  The  lower  end  of  the 
rod  is  usually  of  the  same  form  as  shown  in  Fig.  136. 

Rarely  the  gib  and  key  form  of  connecting-rod  end  as  illus- 
trated in  Fig.  138,  is  found  in  marine  practice. 

In  external  form  marine  conecting-rods  usually  increase 
in  transverse  dimension  from  top  to  bottom.  In  some  cases 
they  are  given  a  uniform  taper  from  one  end  to  the  other,  as  in 


Marine  t-nginetring 

Fig.  138.     Marine   Connecting   Rod  with   Gib   and   Key   Connections. 

Figs.  136-138,  while  in  others  the  extra  metal  is  slabbed  off  on 
the  forward  and  after  sides  until  the  thickness  in  the  fore  and 
aft  direction  is  uniform  from  top  to  bottom. 

As  noted  in  [6],  the  connecting  rod,  in  the  most  advanced 
practice,  is  often  hollow,  a  hole  of  uniform  bore  being  drilled 
from  one  end  to  the  other,  as  shown  in  Fig.  137. 

[9]  Crank  Shafts. 

Modern  marine  crank  shafts  are  of  two  principal  types, 
forged  and  built  up.  Fig.  139  shows  a  portion  of  a  built-up 
crank  shaft.  It  consists,  as  shown,  of  two  crank  urbs  or 
throws,  A  and  B,  one  crank-pin  C  and  two  portions  of  shaft  D, 
E.  Built-up  crank-shafts  are  usually  made  contiuous  for  the 
whole  engine,  and  in  such  case  the  piece  of  shafting  D  connects 


i86 


PRACTICAL  MARINE  ENGINEERING. 


the  crank  shown  with  the  one  next  to  it,  and  thus  serves  as  a 
common  member  for  the  two. 

In  this  type  of  crank-shaft  the  various  sections  of  shaft,  the 
crank-pin  and  the  webs,  are  all  made  separately,  and  then  fitted 
and  secured  together.  This  is  usually  done  by  shrinking  and 
keying  the  various  cylindrical  members  into  the  sections  of  web 
as  shown  in  the  figure. 

Fig.  140  shows  a  section  of  a  forged  crank-shaft.  In  this 
case  a- forging  of  suitable  form  is  made,  and  the  various  parts 
are  then  formed  by  cutting  out  and  machining  this  forging.  In 
many  cases,  moreover,  the  series  of  such  sections  for  the  entire 
engine  are  forged  and  machined  in  one  piece,  the  result  being  a 
continuous  forged  crank-shaft.  In  other  cases  the  section  for 
each  crank,  as  shown  in  the  figure,  is  forged  and  made  sep- 


Fig.  139.     Section    of    Built    Up    Crank    Shaft. 

arately,  the  various  sections  being  then  secured  together  by 
flange  couplings,  as  shown  in  Figs.  140,  141.  The  advantage 
of  making  the  shaft  in  sections  lies  in  the  fact  that  in  many  cases 
the  sections  may  be  made  interchangeable,  and  thus  a  single 
spare  section  is  sufficient  for  the  replacement  of  any  section 
which  may  become  disabled  through  accident,  and  in  any  event 
a  break  will  usually  require  the  refitting  of  a  single  new  section 
instead  of  an  entire  shaft. 

Forged  crank-shafts  are  commonly  used  in  naval  practice, 
and  in  general  where  the  type  of  construction  is  of  specially- 
high  grade  and  the  saving  of  weight  an  important  feature. 
Their  use  in  all  departments  of  marine  practice  seems,  more- 
over, to  be  on  the  increase.  Built-up  crank-shafts,  however,  are 
still  much  used  in  the  mercantile  marine,  especially  where  the 


MARINE  ENGINES. 


187 


conditions  are  easily  fulfilled,  and  their  somewhat  greater 
weight  is  not  a  serious  objection. 

As  noted  in  [6],  the  cylindrical  members  of  marine  engines 
are  often  made  hollow,  especially  in  the  more  advanced  types  of 
design.  Fig.  140  shows  a  crank-shaft  section  with  hollow  pin 
and  shaft.  As  this  feature  was  first  commonly  introduced  in 
connection  with  shafting,  and  is  more  often  met  with  here  than 
elsewhere,  the  advantages  of  such  construction  may  be  now 
considered. 

The  advantages  of  a  hollow  cylindrical  member  such  as  a 
piston-rod,  connecting  rod,  crank-pin,  or  length  of  shafting,  are 
two  in  number,  (i)  It  is  stronger  for  a  given  weight,  or  for  a 
given  strength  less  weight  is  required.  (2)  The  central  core  of 
metal  is  removed,  and  this  is  the  most  liable  to  contain  cracks 
or  flaws,  which  might  in  time  extend  out  into  the  remaining 


Marine  Engi>-Mring    " 


Fig.  140.     Section   of   Forged    Crank   Shaft. 

metal,  and  thus  seriously  weaken  the  member.  Furthermore, 
the  hole  gives  opportunity  for  the  inspection  of  the  metal  on  the 
inside,  and  thus  increases  the  opportunity  for  the  detection  of  a 
flaw  which  might  not  extend  to  the  outer  surface,  or  which 
might  there  be  so  small  as  to  be  overlooked. 

For  cross-breaking  or  for  torsion  the  metal  in  the  ii-- 
terior  of  a  cylindrical  member  is  of  comparatively  small  value. 
Thus  in  a  lo-inch  shaft,  the  inner  core  5  inches  in  diameter  is 
worth  no  more  than  a  shell  of  metal  about  .16  inch  thickness 
lying  next  the  outer  surface.  Or,  as  a  further  illustration,  a  16- 
inch  shaft  with  a  lo-inch  hole  is  equal  to  a  1 5-inch  solid  shaft. 
In  other  words,  a  shell  of  metal  1-2  inch  in  thickness  all  around 
added  on  the  outside  of  the  1 5-inch  shaft  will  make  up  for  the 
removal  of  the  inner  core  of  10  inches  diameter.  In  the  latter 
case  the  hollow  shaft  would  weigh  about  65  per  cent  of  the 
equivalent  solid  shaft.  The  saving  in  weight  for  a  desired 


i88 


PRACTICAL  MARINE  ENGINEERING. 


strength  may  thus  be  very  considerable,  but  it  is  probable  that 
the  advantages  noted  above  under  (2)  are  of  still  greater  im- 
portance, and  in  some  cases  might  justify  the  added  cost  of 
making  the  member  hollow  where  such  addition  could  not  be 
justified  by  the  saving  of  weight  only. 


Fig.  141.     Detail  of  Flange   Coupling  and   Bolt. 

[10]  I/ine  Thrust  and  Propeller  Shafts. 

From  the  crank-shaft  the  motion  is  carried  on  to  the  pro- 
peller by  means  of  a  number  of  lengths  or  sections  of  shafting 
according  to  the  distance  from  the  engine  to  the  stern  of  the 
ship.  Of  these  sections  the  one  to  which  the  propeller  is  at- 
tached is  known  as  the  propeller  shaft.  One  length  must  also 

I 


Fig.  142.     Flexible    Coupling. 

be  specially  fitted  to  transmit  the  forward  thrust  to  the  thrust 
bearing  and  thence  to  the  ship.  This  section  is  known  as  the 
thrust  shaft.  Other  intermediate  lengths  form  the  line  shafting. 
These  various  lengths,  with  the  exception  noted  below,  are 
usually  connected  by  flange  couplings,  as  in  Figs.  140,  141.  The 
coupling  from  the  engine  to  the  next  section  of  shafting  aft  is 


MARINE  ENGINES. 


189 


often  made  of  such  form  as  to  allow  a  certain  degree  of  flexi- 
bility between  the  line  shafting  and  the  crank  shaft.  A  form  of 
such  coupling  is  shown  in  Fig.  142.  One  of  the  coupling  flanges 
is  faced  off,  as  shown  like  the  segment  of  a  sphere,  with  a  ball 
and  socket  joint  at  the  center  to  keep  the  two  parts  in  line.  The 
coupling  bolts  are  then  set  up  with  nuts  bearing  on  some  form 
of  spring  washer  which  will  take  up  the  slack  as  the  shaft  re- 
volves, even  when  not  exactly  in  line.  The  action  of  the  coup- 
ling will  be  readily  seen  from  a  study  of  the  figure.  Various 
other  styles  of  coupling  are  in  use,  but  the  one  shown  will  suffi- 
ciently illustrate  the  principles  involved. 

The  thrust  shaft  will  more  naturally  find  its  description 
with  the  thrust  bearing.  See  [  1 1  ] . 

The  propeller  shaft  is  formed  with  the  after  end  tapered 


Marine  Enyinetring 


c 
Fig.  143.     Outboard  Shaft  for  Twin  Screw  Ship. 


and  fitted  with  screw  thread  for  a  nut,  as  shown  in  Fig.  I43C. 
The  propeller  is  fitted  with  a  corresponding  taper,  and  is  held 
in  place  by  a  nut  and  prevented  from  turning  on  the  shaft  by  one 
or  more  keys,  as  indicated  in  the  figure. 

In  the  case  of  twin  screws,  where  the  propeller  shafts  pass 
outside  the  skin  of  the  ship  some  distance  forward  of  the  stern» 
it  often  becomes  necessary  to  form  the  outboard  shaft  in  more 
than  one  length,  coupled  together  by  flange  couplings  as  above 
described.  In  all  cases  it  is  necessary  to  form  one  end  of  the 
section  of  shaft  which  passes  through  the  skin  of  the  ship  with 
a  plain  end,  so  that  it  can  be  passed  through  'the  outboard  bear- 
ing as  described  in  [n].  In  cases  therefore  where  the  propeller 


ipo  PRACTICAL  MARINE  ENGINEERING. 

cannot  be  attached  directly  to  the  plain  end,  as  in  single  screw 
ships,  it  becomes  necessary  to  provide  a  special  form  of  socket 
coupling  connecting  the  after  end  of  the  last  inboard  length  of 
shafting  with  the  forward  end  of  the  length  which  passes 
through  the  ship.  The  general  plan  of  this  arrangement  is 
shown  in  Fig.  I43b,  and  the  details  of  the  coupling  in  Fig.  144. 
Such  couplings  vary  somewhat  in  detail,  but  the  form  shown  in 


'Marine  Enginetring 


SECTION  ON  C-D 


Fig.  144.    Detail   of   Socket    Coupling. 


the  figure  will  serve  to  illustrate  the  type.  It  consists,  as  shown, 
of  the  enlarged  end  of  the  inboard  shaft,  in  which  is  bored  out 
a  tapering  socket  of  appropriate  size  to  take  the  tapered  for- 
ward end  of  the  first  outboard  length  of  shaft.  The  two  are 
then  secured  together  by  keys  and  locking  ring,  as  shown  in  the 
figure. 

[11]  Bearings. 

The  various  types  and  forms  of  bearing  and  bearing  surface 
to  be  found  in  a  marine  engine  may  be  conveniently  examined 
under  one  heading. 

(i)  Crosshead  and  Guides.  The  stationary  part  of  this  bear- 
ing has  been  already  referred  to  in  [2],  and  as  there  noted  is 
usually  of  a  hard  and  fine  grained  cast  iron.  The  moving  sur- 
face on  the  crosshead  is  usually  of  brass,  bearing-bronze  or 
white  metal.  When  of  brass  or  bronze  it  is  in  the  form  of  a 
bearing  piece  secured  to  the  crosshead,  as  shown  in  Fig.  130. 
When  of  white  metal  a  suitable  slab  of  brass,  cast  i-on  or  cast 
steel,  with  shallow  pockets  formed  in  its  surface,  forms  the  bear- 
ing piece.  These  pockets  have  slightly  overhanging  edges,  and 
into  them  molten  white  metal  is  run,  the  general  layout  and 
arrangement  being  similar  to  that  for  the  main  pillow  block 
bearings  shown  in  Fig.  146.  The  white  metal  is  then  machined 
down  to  a  bearing  surface,  in  some  cases  being  hammered  with 
a  round  pene  hammer  in  order  to  compress  or  harden  the  metal. 


MARINE  ENGINES. 


191 


The  spaces  between  the  pockets  thus  become  spaces  between 
the  sections  of  white  metal,  and  serve  for  the  circulation  and 
supply  of  oil  to  all  parts  of  the  bearing  surface.  In  some  cases 
shallow  channels  or  oil  grooves  are  cut  in  the  guide  surface  or 
stationary  part  as  well,  but  this  is  the  least  necessary  with  the 
arrangement  of  white  metal  as  described. 

Liners  or  packing  pieces  are  often  placed  between  the  bear- 
ing piece  and  the  crosshead,  so  as  to  allow  for  adjustment  and 
take  up  in  case  of  wear. 

(2)  Crosshead  Pins.  The  general  arrangement  for  the 
bearings  are  indicated  in  Figs.  133,  136,  137.  The  crosshead 


Marine  Engineering 
SECTION  THROUGH  A-S 

Fig.  145.     Main  Pillow  Block,   Cap. 


SECTION  THROUGH  C-D 


pins  are  steel,  and  the  bearing  surface  is  brass,  bronze  or  white 
metal.  The  bearing  pieces  are  two  in  number,  forming  between 
them  the  hollow  cylindrical  bearing,  and  are  held  in  place  by 
steel  caps  as  shown.  From  the  fact  that  in  former  practice  such 
bearing  pieces  were  almost  universally  made  of  some  grade  of 
brass,  they  are  still  usually  known  as  brasses. 

When  white  metal  is  used  it  may  be  fitted  in  the  same  gen- 
eral manner  as  above  described  for  the  crosshead  slides,  or  in 
some  cases,  especially  for  small  surfaces,  the  white  metal  sec- 
tions are  turned  down  until  a  continuous  bearing  surface  is  ob- 
tained on  both  white  metal  and  brass.  For  the  distribution  of 


IQ2 


PRACTICAL  MARINE  ENGINEERING 


oil,  grooves  or  channels  are  then  cut  to  serve  in  place  of  the 
channels  between  the  sections  of  white  metal,  as  in  Fig.  146. 

(3)  Crank  Pin.    The  usual  arrangement  of  this  bearing  is 
sufficiently  shown  in  Figs.   136,   137.     In  modern  practice  the 
material  used  is  commonly  white  metal  in  a  brass  backing  or 
bearing  piece,  as  already  described.     In  older  practice  brass  or 
bronze  was  commonly  employed. 

(4)  Pillow  Block  or  Crank  Shaft  Bearings.     The  usual  ar- 
rangements are  shown  in  Figs.  120,  145,  146.     Here  likewise 
in  modern  practice  the  usual  surface  is  white  metal  in  a  brass 
backing  piece.     In  all  bearings  for  cylindrical  elements,  as  the 


^-Hjj^' 


SECTION  ON  C-D 


SECTION  ON 

Fig.  146.     Main  Pillow  Block  Bearing. 


crosshead  pin,  crank-pin,  crank-shaft,  etc.,  the  two  brasses  are 
held  from  separating  by  a  cap  and  bolts  as  shown,  and  from 
pinching  the  pin  or  shaft  too  tightly  by  filling  pieces  or  liners. 
These  by  adjustment  allow  of  take  up  for  wear.  In  modern 
practice  the  lower  pillow  block  brass  is  often  made  in  the  form 
of  a  half  cylinder,  as  shown  in  Fig.  146,  so  that  by  the  removal 
of  the  cap  and  upper  brass  the  lower  one  may  be  slid  around 
the  shaft  and  so  removed  for  adjustment  or  repair,  or  a  new 
brass  replaced  without  disconnecting  the  crank  shaft  and  lift- 
ing it  from  its  bearings,  as  is  necessary  when  the  lower  brasses 
are  of  the  shape  shown  in  Fig.  120. 


MARINE  ENGINES. 


193 


(5)  Line-Shaft  or  Spring  Bearings.  In  these  bearings  the 
chief  load  is  the  weight  of  the  shaft,  at  least  so  long  as  the  bear- 
ings and  shaft  are  in  line  and  adjustment.  It  is  therefore  quite 
common  to  provide  for  such  bearings  simply  a  lower  brass  or 
bearing  piece,  usually  in  modern  practice  of  white  metal  backed 
by  brass,  or  in  some  cases  by  cast  iron  or  steel.  A  bearing  cap 
or  cover  is  then  fitted,  not  in  contact  with  the  shaft,  and  serving 


Fig.  147.     Plain  or  Spring   Bearing. 

simply  to  protect  the  bearing  surface  and  to  support  grease 
cups  or  other  lubricating  arrangement.  A  bearing  of  this  type 
is  shown  in  Fig.  147. 

(6)  Thrust-Bearing.  At  this  bearing  the  thrust  coming 
from  the  propeller  is  taken  off  the  shaft  and  transferred  to  the 
ship.  The  length  of  shafting  which  is  specially  fitted  for  this 
purpose  is  known  as  the  thrust-shaft.  The  special  provision  on 
the  thrust-shaft  consists  of  a  series  of  rings  or  collars,  as  shown 


194 


PRACTICAL  MARINE  ENGINEERING. 


in  Figs.  148-150,  while  the  bearing  of  the  type  shown  in  Fig.  149 
has  a  corresponding  series  of  channels  into  which  the  shaft  rings 
enter  when  the  thrust-shaft  is  in  place.  The  bearing  thus  comes 
on  the  forward  faces  of  the  shaft  rings  and  after  faces  of  the  in- 
termediate bearing  rings  when  the  propeller  is  turning  ahead, 
and  vice  versa  when  backing.  The  faces  of  the  bearing  rings 
are  usually  of  white  metal,  thus  giving  a  steel  on  white  metal 
pair  of  surfaces.  In  order  to  take  the  weight  of  the  thrust-shaft, 
a  support  of  brass  or  white  metal  of  the  usual  spring  bearing 
form  is  usually  provided  at  the  forward  and  after  ends  of  the 
bearing  casing.  The  casing  is  furthermore  commonly  made  in 
the  form  of  a  rectangular  box,  so  that  it  can  be  filled  with  oil  and 
thus  flood  the  bearing  with  lubricant.  Where  the  shaft  passes 
through  the  ends  of  the  casing,  a  stuffing-box  or  form  of  pack- 
ing ring  is  provided  to  prevent  the  oil  from  leaking  through.  At 
the  bottom  of  the  casing  a  hollow  space  is  often  provided  con- 
necting freely  with  the  general  oil  receptacle  above,  and  through 


c 



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Marine  Engineering 

Fig.  148.    Thrust    Shaft. 

which  a  pipe  of  copper  or  thin  brass  is  led  back  and  forth. 
Through  this  pipe  cold  water  is  circulated  for  cooling  down  the 
oil,  and  thus  absorbing  the  heat  of  the  bearing.  The  base  of  the 
bearing  is  secured  to  the  ship  through  a  seating  specially 
strengthened  and  stiffened  to  take  the  thrust  from  the  shaft  and 
thus  transfer  it  to  the  structure  of  the  ship. 

In  Fig.  150  is  shown  a  bearing  somewhat  more  modern  in 
type  and  very  commonly  met  with  in  present  day  practice.  It  is 
known  as  the  horseshoe  collar  bearing.  The  shaft  is  fitted  the 
same  as  in  Fig.  149,  but  the  bearing,  instead  of  being  fitted  with 
series  of  fixed  rings  and  intermediate  channels,  is  provided  with 
a  series  of  separate  collars  of  the  form  shown  in  Fig.  151.  These 
collars  are  provided  with  ears  or  lugs  A  and  B,  by  means  of 
which  they  are  carried  on  side  rods  attached  to  the  bearing 
casing,  as  shown  in  Fig.  150.  These  lugs  in  turn  bear  against 
adjusting  nuts  on  the  side  rods  as  shown.  In  operation  the 
thrust  is  transferred  from  the  shaft  rings  to  the  faces  of  the  col- 


MARINE  ENGINES. 


195 


196 


PRACTICAL  MARINE  ENGINEERING. 


lars,  thence  through  the  lugs  and  nuts  to  the  side  rods,  thence 
to  the  bearing  casing,  and  thence  to  the  ship. 

It  is  readily  seen  that  this  arrangement  allows  of  the  indi- 
vidual adjustment  of  each  collar  as  may  be  required  by  wear, 
or,  if  need  be,  of  its  removal  and  replacement  by  a  spare  collar 
even  when  under  way,  and  without  interfering  with  the  action  of 
the  other  parts  of  the  bearing. 

The  collars  are  usually  of  cast  steel,  or,  in  some  cases,  of 
brass  or  bronze,  and  the  bearing  surface  of  white  metal,  carried 
in  pockets,  as  explained  above. 


Marine  £ngiiieerinf 

Fig.  151.     Detail  of  Collar  Thrust  Bearing. 

The  arrangement  of  the  casing  as  a  receptacle  for  oil,  the 
provision  for  spring  bearings  at  the  ends,  and  the  provision  of 
circulating  pipes  for  cooling  water,  are  similar  to  those  above 
described  in  connection  with  Fig.  149. 

The  thrust  bearing  is  variously  located.  In  some  cases  it  is 
placed  immediately  aft  of  the  engine  with  its  base  connected 
directly  to  the  engine  bed-plate.  In  other  cases  it  is  placed  at 
the  after  end  of  the  inboard  shaft,  or  just  forward  of  the  after 
shaft-alley  bulkhead,  and  in  others  at  some  intermediate  point. 

(7)     Stern  Bearing,    The  general  arrangement  of  the  stern 


MARINE  ENGINES. 


1 37 


bearing  for  a  single  screw  ship  is  shown  in  Fig.  152.  The  en- 
tire distance  through  the  stern  of  the  ship  from  the  stern-post 
to  the  after  bulkhead  of  the  shaft  alley  is  lined  with  a  tube  A  B, 
usually  of  cast  iron.  Within  this  are  placed  brass  tubes  C  D, 
each  perhaps  about  one-third  the  total  length.  These  bearing 

tubes  are  provided  with  longitudinal 
channels  slightly  dovetailed  in  sec- 
tion, as  shown  in  the  figure,  and  into 
these  are  forced  blocks  of  lignum 
vitae  for  a  bearing.  The  arrange- 
ment is  therefore  somewhat  similar 
to  that  for  white  metal,  as  described 
above,  except  that  lignum  vitae  is 
substituted  for  white  metal,  and  is 
placed  in  continuous  channels  run- 
ning the  entire  length  of  the  bearing 
tube  with  intermediate  spaces  be- 
tween. The  shaft  itself  is  cased  with 
a  brass  sleeve  or  casing,  so  that  the 
bearing  surfaces  are  brass  on  lignum 
vitae.  It  is  found  by  experience  that 
water  is  a  lubricant  for  such  a  pair  of 
surfaces,  and  it  is  chiefly  for  this  rea- 
son that  lignum  vitae  is  so  common- 
ly used  as  the  material  for  the  sta- 
tionary part  of  the  bearing.  The 
brass  sleeve,  which  preferably  ex- 
tends the  whole  length  of  that  part  of 
the  shaft  within  the  tube,  also  pro- 
tects the  shaft  from  corrosion.  This 
part  of  the  shaft  is  known  either  as 
the  tail  shaft  or  propeller  shaft.  It  is 
usually  made  a  little  larger  than  the 
line  shaft  to  provide  for  corrosion, 
and  also  for  the  more  violent  shocks 
to  which  it  is  subject.  At  the  forward 
end  of  the  tube  A  is  fitted  a  stuffing- 
box,  through  which  the  shaft  passes 
to  the  after  end  of  the  shaft  alley. 
At  the  after  end  of  the  tube  the 
water  enters  freely  through  the 


198 


PRACTICAL  MARINE  ENGINEERING. 


spaces  between  the  lignum  vitae  and  flows  forward,  thus  serv- 
ing to  cool  and  lubricate  the  bearing.  At  the  forward  end  the 
stuffing-box  prevents  leakage  through  into  the  ship.  It  is  de- 
sirable, however,  to  fit  a  small  pipe  and  cock  so  that  water 
may  be  drawn  from  the  tube  as  desired,  in  order  to  judge  by 
its  temperature  as  to  the  condition  of  the  bearing.  Instead  of 
a  pipe  and  cock  the  stuffing-box  follower  is  sometimes  loos- 
ened up  so  as  to  allow  a  sufficient  leakage  to  insure  circula- 
tion through  the  tube,  and  to  serve  as  an  index  of  the  condi- 
tion of  the  bearing. 

In  some  cases,  instead  of  water  lubrication,  the  after  end  of 
the  stern  tube  is  closed  against  the  water,  and  the  tube  is  filled 


Fig.  153.     Stern  Brackets. 

with  heavy  oil  or  tallow.  Or. if  desired  a  stand  pipe  may  be  run 
up  to  a  sufficient  height,  so  that  when  filled  with  oil  it  will  pro- 
duce a  pressure  in  the  tube  slightly  greater  than  that  of  the 
water  outside,  and  thus  the  leakage  will  be  outward  rather  than 
inward.  With  oil  lubrication  the  lignum  vitae  bearing  surface  is 
replaced  by  white  metal. 

In  small  craft  the  steel  shaft  without  casing  is  often  fitted 
directly  in  a  brass  bushing  or  bearing.  In  such  case  oil  lubri- 
cation is  to  be  preferred,  but  very  commonly  the  bearing  is  left 
to  run  with  such  lubrication  as  the  water  can  provide. 

For  twin  screw  ships,  as  shown  in  Fig.  143,  the  same  gen- 
eral arrangement  'is  used,  except  that  the  length  of  the  tube 


MARINE  ENGINES. 


199 


where  it  passes  through  the  skin  of  the  ship  is  shorter,  and  fre- 
quently the  lignum  \itae  bearing  extends  the  entire  length  in- 
stead of  over  a  part  of  the  forward  and  after  ends.  A  similar 
form  of  bearing  is  also  provided  in  the  shaft  brackets  or  struts 
just  forward  of  the  stern  post.  The  general  form  of  such  brack- 


TCP  VIEW 


LONGITUDtNAL    SECTION 
Fig.  154.     Stern  Bracket  Bearing. 

ets  is  shown  in  Fig.  153.  On  each  side  is  a  heavy  steel  casting 
secured  firmly  at  top  and  bottom  to  the  structure  of  the  ship, 
and  carrying  at  the  apex  a  boss  for  the  bearing,  as  shown  in 
Fig.  154.  This  bearing  is  formed  by  a  tube  carrying  lignum 
vitae  strips  as  previously  described,  and  in  this  way,  with  twin 
screws,  the  extreme  after  ends  of  the  shafts  are  supported. 

Sec.  22.    WESTERN  RIVER  BOAT  PRACTICE. 

The  peculiar  conditions  existing  on  the  western  rivers  of 
the  United  States  have  resulted  in  the  development  of  a  special 
type  of  boat  and  propelling  machinery.  In  the  early  days  of 
river  navigation  the  raft  was  first  employed,  and  then  came  the 
flatboat,  which  has  stood  as  the  type  of  all  later  developments. 
On  the  rivers  where  at  certain  seasons  of  the  year  the  water  is 
shallow,  the  current  swift  and  the  channel  narrow  and  tortuous, 
the  usual  style  of  keel  boat  would  be  of  small  service,  while  the 
light  draft  flat  bottom  craft  seems  admirably  adapted  for  navi- 
gation under  such  difficulties. 


200 


PRACTICAL  MARINE  ENGINEERING. 


Of  the  two  varieties  of  boat,  side  wheel  and  stern  wheel, 
the  latter  is  preferred  as  on  the  whole  the  better  suited  to  the 
all-around  conditions  of  river  navigation,  and  the  flat-bottomed 
stern  wheel  craft  may  to-day  be  considered  as  the  typical  boat 
for  western  river  navigation.  Indeed  this  type  of  boat  has  met 


*V«rwte  Engineering 


Fig.  155.     Western  River  Engine,  Elevation  and  Section  through  Valve  Chests. 

with  much  favor  for  river  navigation  in  all  parts  of  the  world,  and 
especially  in  South  America,  where  they  are  largely  employed. 
The  type  of  engine  used  on  western  river  boats  is  shown  in 
Figs.  155-157.  It  is  horizontal  and  of  the  simple  non-con- 
densing type.  Two  such  engines  are  usually  employed,  .one  on 
each  side  placed  close  to  the  guards,  with  the  axis  of  the  cylin- 


Fig.  156.     Western   River  Engine.     Top  View. 

ders  fore  and  aft,  and  with  the  connecting-rods  coupled  to  the 
cranks  on  the  stern  wheel  paddle  shaft. 

The  cylinders  are  of  relatively  small  diameter  and  long 
stroke,  the  dimensions  in  a  typical  case  being  24-inch  diameter 
by  96-inch  stroke.  The  most  peculiar  feature  of  the  engine, 
however,  is  found  in  the  valve  gear.  The  valves  themselves  are 
usually  of  the  double-beat  poppet  form,  as  shown  in  Fig.  155, 


MARINE  ENGINES. 


201 


and  each  cylinder  is  provided  with  four,  two  for  steam  and  two 
for  exhaust.  These  valves  are  actuated  by  a  cam  valve  gear 
mechanism,  as  briefly  described  below. 

The  steam  valves  with  their  connecting  pipes  are  located 
on  one  side  of  the  cylinder,  while  the  exhaust  valves  and  con- 
nections are  on  the  other  side.  Each  set  of  valves  is  operated 
by  separate  rocking  cams  or  levers,  which  receive  their  motion 
through  rockers  and  connections  from  a  special  cam  located  on 
the  main  paddle  shaft. 

The  cam  type  of  valve  gear  possesses  peculiar  advantages, 
especially  for  long  stroke,  slow  revolution  engines  such  as  are 
used  in  these  cases.  The  motion  of  the  valve  may  thus  be  made 
intermittent,  giving  a  quick  opening  and  closure,  with  interme- 


Marine  Enyliieering 

Fig.  157.    Western   River  Engine,   End  View  and   Section   Showing  Valves. 

diate  periods  of  rest  or  very  slow  motion.  It  is  also  peculiarly 
adapted  to  the  elastic  movements  of  the  boat  during  the  process 
of  loading,  unloading,  etc.,  movements  which  continually  vary 
the  distance  between  the  main  shaft  and  rock  shaft,  and  which, 
with  almost  any  other  type  of  gear,  would  introduce  serious  dis- 
turbance into  the  movement  of  the  valve  and  the  distribution  of 
the  steam. 

For  the  operation  of  these  valves  in  the  common  type  of 
gear  two  cams  are  used ;  one  known  as  the  full  stroke  cam  and 
one  as  the  cut-off  cam.  When  the  engine  is  in  full  gear  the  full 
stroke  cam  operates  all  four  valves,  raising  one  exhaust  and 
one  receiving  valve  at  opposite  ends  of  the  cylinder  at  the  same 
moment,  and  alternately  at  each  end,  thus  distributing  the  steam 


202 


PRACTICAL  MARINE  ENGINEERING. 


as  required  to  carry  the  piston  back  and  forth  continuously. 
The  one  cam  does  all  the  work  in  the  full  gear  motion  of  the 
engine  both  ahead  and  astern,  and  is  hence  in  its  neutral  posi- 
tion when  the  crank  is  at  its  dead  point.  The  cut-off  cam  is  so 
arranged  as  to  be  hooked  on  after  the  full  stroke  cam  has  given 


Fig.  158.    Full   Stroke   Cam  with  Yoke. 

headway  to  the  boat,  and  is  used  in  the  go-ahead  motion  only. 
This  cam  is  so  designed  that  the  steam  is  cut  off  at  any  desig- 
nated point  in  the  stroke,  as  at  J^,  JH$,  3^,  etc. 

The  form  of  a  full  stroke  cam  with  its  yoke  is  shown  in 
Fig.  158,  and  of  a  ^  stroke  cut-off  cam  in  partly  dotted  lines. 


Fig.  159.    Full  Stroke  Cam. 

In  Fig.  159  is  shown  the  usual  type  of  construction  of  the  full 
stroke  cam,  and  in  Fig.  160  similarly  the  3,4  cut-off  cam. 

With  this  arrangement  of  gear  the  exhaust  is  opened  and 
closed  just  at  the  end  of  the  stroke,  and  hence  neither  early  ex- 
haust opening  nor  closure  for  cushion  can  be  obtained.  A 


MARINE  ENGINES. 


203 


means  of  obtaining  the  former  has  been  found  by  blocking  up 
the  exhaust  lifters  somewhat,  so  that  the  valve  will  be  slightly 
open  when  the  engine  is  on  the  dead  point. 

This  insures  an  earlier  opening  of  the  exhaust  and  so  clears 
the  cylinder  for  the  return  stroke,  but  it  gives  likewise  a  later 
exhaust  closure,  so  that  with  the  engine  on  the  center  both  ex- 
haust valves  are  slightly  open,  and  in  full  gear  operation  a  slight 
"blow  through"  will  occur.  This  disappears,  however,  when  the 
cut-off  cam  is  engaged,  because  the  opening  movement  of  the 
latter  is  much  slower  than  that  of  the  full  stroke  cam. 

Various  modifications  of  this  simple  cam  gear  have  been 
introduced  with  a  view  of  improving  the  general  operation, 
especially  by  the  provision  of  means  for  obtaining  both  steam 
and  exhaust  lead  and  compression,  as  well  as  independent  move- 
ments for  the  go-ahead  and  backing  motions. 


Fig.  160.    Three  Quarter  Cut-off  Cam. 

In  the  Sweeney  valve  gear  two  full  stroke  cams  are  em- 
ployed, one  for  go  ahead  and  one  for  backing,  each  set  so  as  to 
give  suitable  exhaust  lead  and  compression,  while  a  separate 
cut-off  cam  is  fitted  for  the  go-ahead  motion. 

The  crossheads  of  these  engines  are  usually  of  the  locomo- 
tive type,  with  long  brass  gibs  bearing  on  the  top  and  bottom 
guides.  The  connecting-rods  are  commonly  of  wrought  iron  or 
wood,  with  iron  or  steel  fittings,  and  form  one  of  the  most  pe- 
culiar features  of  these  engines.  Wood  is  often  thus  preferred 
over  metal  because  it  seems  to  be  better  capable  of  standing  the 
shocks  and  peculiar  twisting  strains  which  come  upon  the  rod, 
and  in  spite  of  the  strangeness  of  the  combination,  we  find  in 
some  modern  boats  a  fluid  compressed  nickel  steel  paddle  shaft 
with  a  wooden  connecting-rod.  The  rods  are  very  long,  fre- 
quently as  much  as  eight  times  the  crank,  and  the  best  rods  are 


204  PRACTICAL  MARINE  ENGINEERING. 

made  of  Oregon  fir,  reinforced  with  iron  straps  which  are  let 
into  the  body  of  the  rod  and  through  bolted.  The  ends  of  the 
rods  are  fitted  with  brass  boxes  with  straps,  gibs,  keys,  etc.,  in 
the  usual  manner  of  fitting  up  such  form  of  rod,  and  as  illus- 
trated in  Fig.  138. 

In  some  cases  of  modern  river  boats  on  the  Pacific  Coast 
many  changes  have  been  introduced  looking  toward  a  closer 
approach  to  usual  marine  practice.  In  a  typical  example  of  such 
improved  practice  the  engines  are  horizontal  tandem  compound, 
the  high-pressure  cylinder  having  piston  valves  and  the  low- 
pressure  cylinder  slide  valves,  both  operated  by  excentrics  and 
link  work  in  the  usual  way.  In  this  case  there  are  two  engines 
developing  about  1,500  I.  H.  P.  each.  The  cylinders  are  22^/2  in. 
and  38^4  in.  diameter,  with  a  stroke  of  8  feet,  and  are  intended 
to  make  thirty  revolutions  per  minute. 

The  crank  shaft  for  such  engines  is  built  up  in  structure, 
the  two  cranks  being  separately  forged  and  secured  to  the  pad- 
dle shaft  by  shrinking  and  appropriate  keys.  The  shaft  is 
usually  fitted  with  hexagonal  bosses  where  the  wheel  flanges 
are  to  be  secured.  The  latter  are  usually  of  cast  iron,  heavily 
ribbed  and  reinforced  by  wrought  iron  bands  shrunk  on  their 
hubs  and  outer  circumference.  These  flanges  are  fitted  to  the 
hexagonal  bosses  on  the  shaft,  and  are  secured  with  suitable 
keys.  They  are  provided  on  one  face  with  sockets  for  the  wheel 
arms,  which  are  of  wood.  These  latter  are  further  strengthened 
by  circular  bands  of  iron  bolted  near  the  outer  ends,  and  also  by 
oblique  bracing  which  is  worked  between  them. 

The  buckets  are  also  of  wood,  2-inch  oak  plank  of  suitable 
width  and  length  being  a  standard  material.  They  are  secured 
to  the  wheel  arms  by  special  clamp  bolts,  and  are  so  located 
relative  to  the  draft  of  the  boat  as  to  be  immersed  only  some 
4  to  6  inches  when  the  steamer  is  running  light.  In  some  cases 
the  buckets  are  divided  at  the  center,  forming  really  two  sets, 
staggered  with  reference  to  each  other,  and  thus  reducing  the 
shock  of  the  wheel  as  it  enters  the  water. 

DOCTOR. 

This  peculiar  feature  of  western  river  practice  as  illus- 
trated in  Fig.  161,  is  a  combination  of  feed  pump  and  feed  water 
heater.  As  here  shown,  the  doctor  consists  of  a  vertical  beam 
engine  with  crank  and  flywheel  operating  four  pumps.  Two  of 


MARINE  ENGINES. 


205 


these  are  simple  lift  pumps  drawing  water  from  the  river  and 
delivering  it  into  the  heating  chambers  overhead,  while  the 
other  two  are  feed  pumps  proper,  taking  their  supply  from  the 
heaters  and  forcing  the  water  into  the  main  boilers.  Each  lift 
and  force  pump  is  designed  of  sufficient  capacity  to  supply  the 
entire  battery  of  boilers,  so  that  one  of  either  kind  may  be  dis- 


Marine  Engineering 

Fig.  161.    Western  River  Boat  "Doctor." 

connected  for  examination  or  repair  without  disturbing  the 
regularity  of  boiler  feed  supply.  The  various  parts  of  the  ma- 
chine are  erected  on  a  deep  cast  iron  base  plate  which  contains 
various  ports  and  passages,  forming  the  water  connections  be- 
tween the  various  pumps. 

The  suction  pipe  from  the  river  is  connected  with  a  vacuum 
chamber,  and  communicates  through  a  passage  in  the  base  cast- 


206  PRACTICAL  MARINE  ENGINEERING. 

ing  with  the  suction  side  of  the  lift  pump.  The  discharge  from 
these  pumps  is  then  led  by  other  passages  to  the  columns,  which 
serve  as  discharge  pipes,  supports  for  the  engine  beam  and  for 
the  heaters.  Valves  are  also  located  in  these  columns,  by 
closing  which  the  water  in  the  heaters  may  be  prevented  from 
returning  at  such  times  as  it  is  necessary  to  open  up  a  pump  for 
examination  or  repair. 

The  heaters  themselves  consist  of  wrought  iron  shells  riv- 
eted to  cast  iron  heads,  through  which  the  exhaust  steam  from 
the  main  engines  is  led  on  its  way  to  the  exhaust  pipe.  The  ex- 
haust steam  thus  comes  in  direct  contact  with  coils  of  copper 
pipe  that  lie  in  the  lower  part  of  the  heaters,  and  through  wrhich 
the  feed  water  is  forced  and  finally  discharged  below  a  dia- 
phragm. Beyond  this  the  exhaust  steam  and  water  are  to  some 
extent  in  direct  contact,  the  latter  being  finally  lead  down 
through  the  pair  of  columns  on  the  opposite  side  of  the  machine 
to  the  feed  pump  inlet  valves  in  the  base-plate.  The  head  of 
water  in  the  columns  is  thus  sufficient  to  flood  the  valves  and 
prevent  the  pump  from  missing  stroke,  even  with  the  hottest 
feed  water  which  the  heaters  can  furnish. 

The  lift  pumps  are  fitted  with  long  pistons  having  either 
cup  leather  or  square  gum  packing,  while  the  feed  pumps  are 
of  the  common  plunger  type.  The  pump  valves  are  flat  disks  of 
brass  made  quite  thick  so  as  to  avoid  the  need  of  springs,  and 
also  to  allow  metal  for  re-facing.  The  engine  part  of  the  doctor 
is  very  simple  and  will  call  for  no  special  comment,  consisting 
simply  of  a  steam  cylinder  for  actuating  the  beam  and  thus  giv- 
ing motion  to  the  four  pumps  as  described. 

In  some  cases  of  recent  river  practice  injectors  have  taken 
the  place  of  the  "doctor,"  and  if  they  can  be  depended  upon 
they  are  of  course  much  preferable,  being  easy  to  handle  and 
occupying  little  or  no  space  otherwise  valuable.  While  it  is 
probable  that  they  can  thus  be  used  to  advantage  on  certain  of 
the  upper  portions  of  the  western  rivers,  it  is  hardly  possible 
that  they  could  be  used  at  all  in  many  other  localities  on  ac- 
count of  the  sand  and  grit  which  is  held  in  suspension  by  the 
water,  and  which  would  cut  out  the  injector  tubes  so  rapidly 
that  their  use  would  be  out  of  the  question.  For  this  reason  it 
seems  likely  that  the  "doctor"  will  hold  its  own  in  all  such  locali- 
ties and  that  it  will  continue  to  be  an  important  detail  of  west- 
ern river  practice. 


MARINE  ENGINES. 


207 


Sec.  23.    THE  STEAM  TURBINE. 

Within  the  past  few  years  the  application  of  the  steam  tur- 
bine to  marine  propulsion  has  produced  results  which  have  at- 
tracted world-wide  attention,  and  it  seems  at  present  not  un- 
likely that  the  part  taken  in  the  future  developments  of  marine 

propulsion  b>  this  form  of  mo- 
tor will  be  one  of  increasing  im- 
portance. The  present  develop- 
ment is  represented  by  the  Par- 
sons' steam  turbine  as  fitted  on 
the  Turbinia,  and  later  on  the 
British  torpedo-boat  destroyers 
Cobra  and  Viper,  and  Clyde 
passenger  steamer  King  Ed- 
ward. 

This  type  of  motor,  one  form 
of  which  is  represented  in  Fig. 
162,  consists  of  a  cylindrical 
case  carrying  rings  of  inwardly 
projecting  oblique  guide  blades, 
while  within  these  revolves  a 
shaft  carrying  rings  of  outward- 
ly projecting  oblique  blades. 
There  is  a  clearance  of  about 
1-16  inch  between  the  successive 
rings  of  blades  and  guides,  and 
between  the  ends  of  the  former 
and  the  case,  and  the  ends  of  the 
latter  and  the  body  of  the  shaft. 
There  is  thus  left  between  the 
shaft  and  the  case  an  annular 
space  filled  with  alternate  rings 
of  blades  attached  to  the  shaft 
and  guides  attached  to  the  case. 
The  steam  when  admitted  passes 
first  through  a  ring  of  fixed 
guides  by  means  of  which  it  is 
given  a  rotational  motion,  and 
then  projected  on  to  the  first 
ring  of  blades.  It  is  then  thrown 
on  to  the  following  ring  of 


208  PRACTICAL  MARINE  ENGINEERING. 

guides,  by  means  of  which  its  direction  is  again  changed,  and  it 
is  then  thrown  in  the  same  direction  as  at  first  upon  the  second 
ring  of  blades,  and  so  on,  passing  from  one  ring  to  the  next, 
and  giving  to  each  a  part  of  its  energy  and  thus  maintaining 
the  rotation  of  the  shaft.  It  must  be  especially  understood  that 
the  steam  in  a  turbine  acts  by  impact  or  reaction,  and  not  by 
pressure.  As  the  steam  rushes  against  the  blades  and  its  direc- 
tion of  flow  becomes  thereby  changed,  it  exerts  a  reaction  on 
the  blades,  and  this  constitutes  the  force  which  produces  the 
rotation.  The  energy  which  the  steam  possesses  in  virtue  of  its 
temperature  and  pressure  cannot  therefore  be  directly  used  in 
the  turbine  as  in  the  common  steam  engine,  but  it  must  first  be 
transformed  into  the  energy  of  motion  as  in  the  rushing  jet. 
This  transformation  is  effected  by  the  gradual  expansion  of  the 
steam  as  it  passes  through  the  turbine.  This  gradual  expansion 
keeps  up  a  continual  transformation  of  heat  energy  into  the 
energy  of  motion,  and  this  energy  is  as  constantly  transferred 
to  the  moving  blades,  and  thus  the  original  heat  energy  of  the 
steam  is  transformed  into  mechanical  work.  In  order  that  the 
expansion  may  be  carried  on  continuously,  the  cross-sectional 
area  occupied  by  the  blades  is  increased  from  time  to  time,  as 
shown  in  the  figure,  thus  making  a  series  of  steps  of  increasing 
diameters  for  the  rings  of  blades  and  guides.  In  a  moderate 
sized  motor  there  may  be  50  to  80  successive  rings  thus  ar- 
ranged in  from  three  to  five  groups. 

The  steam  pressure  acting  on  the  annular  rings  separating 
these  steps,  and  also  on  the  blades  themselves,  would  set  up  a 
severe  end  thrust.  This  may  be  balanced,  as  in  Fig.  162,  by  ar- 
ranging two  sets  of  such  steps  on  the  same  shaft  varying  in  op- 
posite directions,  and  thus  balancing  each  other  in  end  thrust. 

In  another  method  special  disks  are  fitted  on  the  shaft  with 
grooves  in  their  outer  surface,  within  which  project  rings  car- 
ried in  the  frame.  These  rings  and  grooves  form  a  nearly  steam 
tight  joint,  and  the  annular  area  is  so  adjusted  in  amount  that 
the  steam  acting  on  it  will  balance  the  thrust  acting  on  the 
blades  and  corresponding  annular  area  of  the  main  shaft.  In 
addition  a  special  thrust  bearing  is  fitted  for  taking  any  residual 
end  thrust  and  for  making  the  necessary  adjustments. 

The  arrangement  thus  briefly  described  constitutes  a  sim- 
ple turbine.  By  combining  two  or  three  such  in  series  and 
leading  the  steam  from  one  to  another  through  them,  the  so- 


MARINE  ENGINES.  209 

called  compound  turbine  is  formed.  In  a  simple  turbine  the 
steam  may  be  expanded  some  six  or  eight  times,  so  that  by 
compounding  a  total  expansion  of,  say,  30  to  60  could  be  ob- 
tained, and  by  a  triple  combination  a  total  expansion  of  200  and 
more  may  be  effected. 

The  revolutions  of  the  turbine  are  high.  This  is  a  necessity 
of  its  efficient  performance.  The  Turbinia  has  three  each  of 
about  600  to  700  horse  power,  and  the  revolutions  run  up  to 
about  2,000  per  minute.  In  the  Viper  and  Cobra  there  are  four 
turbines,  each  of  about  1,500  H.  P.,  running  at  about  1,200 
revolutions  per  minute.  With  the  former  a  speed  of  about  34 
knots  has  been  reached,  while  with  the  latter  speeds  of  over  35 
knots  were  reached. 

The  efficiency  of  the  compound  type  of  turbine  is  not  very 
different  from  that  of  good  compound  or  triple  expansion  en- 
gines of  the  usual  type.  The  weight  for  the  same  power  is 
somewhat  less,  though  the  difference  is  not  great  when  com- 
pared with  light  reciprocating  engines  forced  in  a  manner  cor- 
responding to  the  conditions  on  these  boats.  In  other  words, 
the  turbine  shows  no  very  great  saving  over  the  weights  of  the 
lightest  types  of  reciprocating  engines  as  designed  for  torpedo 
craft  ancl  fast  launches. 

The  great  advantages  of  the  turbine  are  found  in  its  com- 
pactness and  absence  of  reciprocating  motions,  and  thus  in  the 
entire  absence  of  the  forces  which  cause  vibrations.  With  ex- 
treme speeds  and  in  many  conditions  of  modern  practice  the 
vibration  forces  become  a  serious  question,  and  a  motor  en- 
tirely free  from  them  becomes  immediately  of  great  importance 
in  all  such  cases. 

In  regard  to  questions  of  durability,  maintenance,  liability 
to  derangement  or  accident,  etc.,  the  experience  available  at 
present  is  too  small,  and  we  must  wait  for  the  future  to  answer 
these  and  many  other  questions  which  bear  on  the  applicability 
of  the  turbine  to  the  various  conditions  of  marine  practice. 

Sec.  24.  ENGINE  FITTINGS. 
[i]  Throttle  Valve. 

The  purpose  of  the  throttle  valve  is  to  provide  a  means  for 
quickly  opening  or  closing  the  main  steam-pipe  near  where  it 
connects  with  the  high  pressure  valve  chest,  and  thus  to  provide 
for  the  quick  control  of  steam  to  the  engine  when  stopping  and 


210 


PRACTICAL  MARINE  ENGINEERING. 


starting.  A  great  variety  of  valves  have  been  employed  for  this 
purpose.  The  necessity  for  quick  operation,  especially  by  hand 
gear,  requires  usually  some  form  of  balanced  valve,  though  in 
very  small  sizes  an  ordinary  globe  or  straight-way  or  gate  valve, 
as  shown  in  Figs.  166,  168  may  be  used.  Of  these  the  straight- 
way valve  is  much  to  be  preferred,  as  when  open  it  leaves  prac- 
tically an  unobstructed  passage  for  the  flow  of  the  steam. 

(i)  Gridiron  Valve.  The  gridiron  is  another  form  of  unbal- 
anced valve  sometimes  employed  as  a  throttle.  This  valve,  as 
shown  in  Fig.  163,  consists  of  a  series  of  bars  and  ports  corre- 
sponding to  a  like  series  in  the  valve  chest,  and  giving  a  series  of 
openings  for  the  steam,  wider  or  narrower  according  to  the 
position  of  the  valve.  With  such  an  arrangement  a  considerable 
area  of  opening  may  be  obtained  with  a  comparatively  small 


Fig.  163.     Gridiron   Valve. 


Fig.  164.     Double  Beat  Poppet  Valve. 

movement  of  the  valve,  and  a  screw  or  some  other  form  of  slow 
motion  gear  may  be  employed  without  loss  of  quick  opening 
and  closure.  This  form  of  valve  is,  however,  but  rarely  met  with 
in  modern. practice. 

(2)  Double  Beat  Poppet.    The  double  beat  poppet  valve,  as 
shown  in  Fig.  164,  has  been  much  employed  as  a  form  of  bal- 
anced throttle.     The  upper  disc  is  slightly  larger  in  area  than  the 
lower,  so  that  if  the  live  steam  is  on  the  outside  the  net  load  on 
the  valve  is  that  due  to  the  difference  of  the  two  areas,  and  this 
may  be  made  very  small.    The  resistance  to  opening  is  thus  no 
more  than  can  be  readily  overcome  with  a  direct  hand  gear,  as 
for  example,  a  simple  lever  or  other  like  arrangement. 

The  chief  difficulty  with  this  valve  is  in  keeping  it  tight,  var- 
iations of  temperature  and  the  consequent  expansions  and  con- 
tractions often  tending  to  slightly  unseat  one  disc  or  the  other. 

(3)  Butterfly  Valve.    The  butterfly  valve  has  also  been  wide- 


MARINE  ENGINES. 


211 


ly  used  as  a  balanced  throttle.  It  consists  of  a  disc  of  elliptical 
form  carried  on  a  spindle  and  swinging  within  a  cylindrical 
casing.  When  closed  it  rests  obliquely  on  the  inner  surface  of 
the  casing,  thus  closing  the  passage  around  its  outer  circumfer- 
ence. When  full  open  it  swings  into  a  position  with  its  plane 
lying  along  the  pipe,  thus  leaving  the  passage  nearly  free  for  the 
flow  of  steam.  This  form  of  valve  is  quite  perfectly  balanced, 
but  it  is  difficult  to  keep  tight.  If  the  angle  of  obliquity  with  the 
surface  of  the  casing  is  too  small,  it  may  also  be  liable  to  stick 
fast,  due  to  unequal  expansion  of  the  valve  and  casing.  In  an- 
other form  of  butterfly  valve,  as  shown  in  Fig.  165,  however,  the 


Marine  Enginitrmg 

Fig.  165.     Combined  Stop  and  Throttle  with  Balance  Piston. 

disc  is  circular  and  when  closed  swings  square  across  the  line  of 
flow,  just  fitting  within  a  corresponding  ridge  of  the  casing.  In 
such  case  the  diameter  of  the  opening  must  be  made  enough 
larger  than  that  of  the  disc  to  avoid  the  danger  of  striking,  and 
considerable  leakage  will  usually  result. 

(4)  Disc  Valve  With  Balance  Piston.  A  plain  disc  with  bal- 
ance piston  attached  to  the  stem  is  quite  commonly  employed  in 
modern  practice  for  the  throttle  or  for  the  stop  and  throttle  com- 
bined. Such  an  arrangement  in  combination  with  a  butterfly 
valve  is  shown  in  Fig.  165.  By  this  means  the  pressure  on  the 
piston  nearly  balances  the  load  on  the  valve,  and  it  may  thus  be 
operated  by  hand  gear.  Steam  may  also  be  admitted  back  of 
the  piston  by  a  pipe  with  stop-valve  operated  from  the  working 
platform.  By  this  means  the  disc  may  be  balanced  when  once 
off  the  seat,  and  closure  effected  as  easily  as  opening. 


212 


PRACTICAL  MARINE  ENGINEERING. 


(5)  Power  Operated  Throttle.  In  some  cases1  with  large  en- 
gines the  throttle  is  operated  by  steam  power  instead  of  by  hand, 
steam  being  admitted  to  an  operating  cylinder  by  means  of  a 
hand  lever  or  other  like  arrangement.  Here  the  steam  acts 
upon  an  auxiliary  piston  and  by  suitable  connections  produces 
the  movement  of  the  throttle  as  desired.  In  such  cases  the  con- 
nections are  often  of  the  "floating  lever"  type,  as  in  the  reversing 


Fig.  166.     Globe  Valve. 

gear  described  in  [5,]  so  that  the  valve  will  follow  the  hand  lever 
in  its  movement  back  and  forth,  and  the  combination  becomes 
thus  equivalent  to  a  direct  operation  of  the  throttle  by  hand. 

[a]  Main  Stop  Valve. 

The  throttle  valve  from  its  construction  can  rarely  be  closed 
sufficiently  tight  to  prevent  leakage  of  steam,  often  considerable 
in  amount.  To  provide  a  shut-off  without  sensible  leakage  a 


MARINE  ENGINES. 


213 


stop  valve  is  often  fitted  in  addition.      Such  valves  may  be  of 
various  types,  as  shown  in  Figs.  166,  167,  168. 

(i)  Globe  Valve  ^  This  valve,  as  shown  in  Fig.  166,  consists 
of  a  metal  chamber  of  globular  or  spherical  form  with  flanges  for 
connecting  to  the  line  of  piping.  Within  the  body  is  a  partition 
separating  the  portions  connected  with  the  two  openings,  and  in 
this  partition  is  a  hole  with  conical  seat  upon  which  the  valve 
with  corresponding  conical  face  bottoms  when  closed.  The 
valve  is  attached  to  a  threaded  spindle  which  works  in  a  nut 
either  formed  in  the  neck  which  contains  the  stem,  or  carried 


Marine  Engineering 


Fig.  167.     Angle  Stop  Valve. 

outside  on  a  girder  supported  by  stud  bolts,  as  shown  in  the  fig- 
ure. To  the  end  of  the  stem  a  handle  is  attached,  and  by  this 
means  the  valve  is  opened  or  closed  as  desired.  The  stem  is 
packed  by  means  of  a  stuffing-box  and  soft  packing  compressed 
by  a  gland  of  the  usual  form  as  shown.  In  small  sizes  the  gland 
is  usually  replaced  by  a  form  of  nut  threaded  to  the  neck,  which 
contains  the  stem,  and  compressing  the  packing  between  the  nut 
and  the  bottom  of  the  packing  space. 

(2)  Angle  Valve.     In  this  type  of  valve,  which  is  an  angle 
or  elbow  and  a  valve  combined,  the  seat  and  valve-face,  as  shown 


214 


PRACTICAL  MARINE  ENGINEERING. 


in  Fig.  167,  are  placed  square  across  one  of  the  openings,  thus 
shutting  off  all  flow  through  it  when  the  valve  is  closed.  When 
the  valve  is  opened,  however,  the  passage  is  left  free,  according 
to  the  degree  of  opening,  for  the  flow  of  the  liquid  or  vapor 
around  the  angle  and  on  into  the  following  section  of  pipe. 

When  the  stop  valve  is  of  the  disc  form  it  is  very  commonly 
of  the  angle  type  and  arranged  to  go  in  at  a  turn  of  the  pipe,  as 
shown  in  Fig.  167.  In  this  case  also  the  valve  is  attached  to  a 
bulkhead  and  the  arrangement  will  serve  to  show  the  method  of 


Marine  Engineering 

SECTIONAL  ELEVATION  SECTIONAL  PLAN 

SHOWING  BY-PASS 
Fig.  168.     Gate  Valve. 

carrying  steam  through  a  bulkhead  and  of  making  up  the  joints 
connecting  together  the  steam  pipe,  the  stop  valve  and  the  bulk- 
head plate. 

(3)  Straight-way  or  Gate  Valves.  In  this  form  of  valve, 
which  is  shown  in  Fig.  168,  the  moving  part  consists  of  a  special 
form  of  slide  which  is  moved  by  a  screw  back  and  forth  across 
the  opening  of  the  pipe.  There  are  various  special  forms  and  de- 
vices for  securing  tight  contact  between  the  valve  and  its  seat 
when  closed,  and  thus  making  the  valve  tight  under  steam  pres- 


MARINE  ENGINES.  215 

sure.  The  general  arrangement  of  Fig.  168  will,  however,  serve 
to  show  the  main  features  of  valves  of  this  type.  When  closed 
and  with  pressure  on  one  side  of  the  slide  only,  there  is  some- 
times some  difficulty  in  opening  the  valve.  To  relieve  this  con- 
dition a  small  by-pass,  as  shown,  is  often  fitted.  This  admits 
steam  to  the  farther  side  of  the  valve,  thus  balancing  the  load 
and  making  the  operation  of  opening  much  easier.  In  another 
form  the  valve  slide  is  made  of  two  parts,  hinged  together  and 
with  the  end  of  the  spindle  working  between  them  in  such  way 
that  when  screwed  hard  down  it  is  forced  as  a  wedge  between  the 
two  parts  thus  forcing  them  against  their  seats.  When  the 
handle  is  turned  in  the  reverse  way  the  first  action  is  to  partly 
withdraw  the  stem  from  between  the  two  parts  of  the  slide,  thus 
easing  them  from  their  seats  and  allowing  them  to  be  readily 
withdrawn  as  the  stem  is  turned  farther  back. 

When  the  throttle  takes  the  form  of  a  plain  disc  with  bal- 
ance piston,  as  in  Fig.  165,  no  additional  stop  is  thought  neces- 
sary, and  such  an  arrangement  is  often  known  as  a  combined 
stop  and  throttle  valve.  In  such  case,  however,  a  screw  stem 
may  be  provided  with  connections  for  bringing  it  into  use  when 
closing  the  valve  down  as  a  stop. 

[3]  Cylinder  Drain  Gear  and  Relief  Valves. 

A  certain  amount  of  water  is  likely  to  collect  in  the  steam 
chests  and  cylinders,  either  carried  in  with,  or  condensed  from 
the  entering  steam,  especially  when  warming  up  the  engine  pre- 
paratory to  getting  under  way.  Provision  must  be  made  for 
getting  rid  of  this  water  as  occasion  may  require,  and  to  this  end 
the  so-called  cylinder  drains  and  relief  valves  are  fitted.  The 
drains  are  usually  plain  cocks  piped  up  and  connected  to  the 
parts  to  be  drained,  and  with  the  valve  stems  connected  by 
levers  and  bell-cranks  to  operating  handles  at  the  starting  plat- 
form. The  drains  in  the  bottom  of  the  cylinder  or  valve-chest 
will  naturally  be  placed  at  the  lowest  point  at  which  water  can 
collect,  or  as  near  to  such  point  as  is  practicable.  Those  in  the 
upper  end  of  the  cylinder  will  be  placed  at  such  a  height  that  the 
opening  will  not  be  covered  by  the  piston  when  at  the  top  of 
the  stroke. 

For  small  engines,  auxiliaries,  pumps,  etc.,  the  drain  valves 
are  often  plain  globe  valves  piped  into  the  cylinder  at  convenient 
points,  and  operated  independently  by  hand. 


216  PRACTICAL  MARINE  ENGINEERING. 

The  discharge  of  the  drains  is  piped  away  either  into  the 
bilge,  or  into  a  fresh  water  collecting  tank. 

In  addition  to  such  gear,  which  is  operated  by  hand,  and 
when  judgment  may  calMor  its  use,  it  is  necessary  to  provide 
automatic  relief  valves  for  the  discharge  of  water  in  larger  quan- 
tities should  it  find  its  way  into  the  cylinder  by  priming  or  in 
other  ways.  Such  a  relief  valve  is  in  the  form  of  a  safety  valve, 
and  may  be  set  to  open  at  any  pressure  desired.  Such  valves 
are  sometimes  connected  up  with  operating  levers,  also  led  to 
the  starting  platform,  so  that  they  may  be  operated  by  hand  from 
that  point.  In  such  cases  only  the  one  set  of  valves  is  often 
fitted,  automatic  when  necessary,  and  under  hand  control  when 
desired.  In  some  cases  with  large  engines  a  double  set  of 
automatic  relief  valves  is  furnished,  a  pair  of  large  valves  not 
under  hand  control,  and  a  smaller  pair  under  hand  control,  as 
described  above. 

[4]  Starting  Valves. 

In  order  to  assist  in  starting  the  engine,  especially  if  the 
high  pressure  piston  happens  to  be  on  or  near  the  center,  a  valve 
and  pipe  are  usually  provided  for  admitting  steam  direct  from 
the  steam  pipe  or  high  pressure  valve  chest,  to  the  first  receiver, 
or  intermediate  pressure  valve  chest.  This  will  give  sufficient 
load  on  the  intermediate  pressure  piston  to  start  the  engine,  and 
carry  the  high  pressure  piston  off  the  center,  and  thus  give  the 
engine  a  chance  to  start  in  the  regular  way.  In  case  the  high 
pressure  and  intermediate  pressure  cranks  should  be  opposite, 
and  thus  both  pistons  on  or  near  the  center  at  the  same  time, 
the  auxiliary  pipe  will  lead  to  the  second  intermediate  piston, 
or  to  the  first  cylinder,  whose  piston  is  not  on  the  center  with  the 
high  pressure.  In  some  cases  the  passage  of  the  steam  to  the 
next  cylinder  beyond  the  high  pressure  is  effected  by  the  open- 
ing of  a  valve  connecting  the  steam  and  exhaust  sides  of  the 
high  pressure  valve  chest.  Such  valve  being  opened  the  steam 
finds  its  way  directly  to  the  point  where  it  is  needed. 

Valves  for  this  general  purpose  are  variously  called  pass- 
over,  or  starting  valves,  or  monkey  tails.  They  are  either  in  the 
form  of  a  cock  or  of  a  small  slide  valve,  in  either  case  admitting 
of  full  opening  by  a  single  short  stroke  of  a  convenient  hand 
lever,  to  which  they  are  connected  by  suitable  rods  and  con- 
nections. 


MARINE  ENGINES. 


217 


[5]  Reversing  Gear. 

The  various  links  of  a  Stephenson  valve  gear,  as  will  be 
seen  in  Section  53,  are  connected  by  side  or  bridle  rods  to  arms 
on  the  rock  or  "weigh"  shaft.  To  reverse  or  link  up  with  such 
a  gear,  therefore,  it  becomes  necessary  to  provide  some  means 
for  turning  this  shaft  back  and  forth,  and  for  holding  it  under 
complete  control  at  any  position  desired.  The  form  of  reverse 
gear  most  commonly  employed  in  American  practice  is  of  the 
so-called  "floating  lever"  type,  and  is  illustrated  in  Fig.  169. 

It  consists  of  a  cylinder,  AB,  with  piston  and  rod,  D,  con- 
nected by  a  link  from  E  to  an  arm  on  the  engine  rock  shaft, 
and  thus  connecting  with  the  links. 


Fig.    169.      Floating    Lever    Reverse    Gear. 

As  the  piston  is  moved  back  and  forth  by  the  steam  this  arm 
will  evidently  be  carried  with  it,  and  the  various  Stephenson 
links,  or  like  parts  of  other  types  of  valve  gear,  will  be  moved 
as  desired,  each  through  its  connection  with  the  rock-shaft.  The 
steam  to  the  cylinder,  AB,  is  controlled  by  a  slide  valve,  V,  either 
plain  or  of  the  piston  type.  This  valve  has  very  small  lap  so 
that  from  the  position  when  covering  both  ports  but  slight 
movement  is  needed  to  uncover.  To  the  stem  of  the  valve  is  at- 
tached a  link,  LI,  which  at  the  latter  point  is  joined  to  a  bar,  KH. 
The  lower  end,  H,  of  this  bar  is  attached  to  a  lug,  Q,  on  the 
piston  rod,  and,  therefore,  moves  with  the  piston.  The  upper 
end,  K,  is  connected  through  a  link,  KN,  to  a  hand  lever,  which 
is  provided  with  means  for  clamping  in  any  position  desired. 


2i8  PRACTICAL  MARINE  ENGINEERING. 

Suppose  now  the  gear  in  the  position  shown  and  with  the 
valve  covering  both  ports.  Let  the  hand  lever  be  moved  so  as 
to  throw  KN  to  the  left.  For  the  moment  H  will  be  a  fixed 
center,  and  with  the  connections  shown  the  valve  will  be  moved 
to  the  left  also.  With  this  arrangement  of  connections  an  in- 
side valve  (Section  46  [7] )  must  be  used,  and,  therefore,  steam 
will  be  admitted  to  the  left  hand  end  of  the  cylinder,  AB,  and 
the  piston  forced  to  the  right.  Let  the  hand  lever,  carrying 
with  it  the  valve,  be  thus  moved  over  a  certain  distance  and  then 
held  or  clamped  there,  thus  fixing  NK.  The  point,  K,  will  thus 
become  for  the  time  a  fixed  center,  and  the  movement  of  H  to 
the  right  will  carry  the  valve  in  the  same  direction,  and  thus 
finally  close  the  ports,  shutting  off  the  supply  of  steam  at  one  end 
and  closing  the  exhaust  at  the  other.  '  The  movement  of  the 
piston  will  thus  be  stopped  and  the  gear  will  be  held  in  the  po- 
sition reached.  It  is  clear  that  for  every  position  of  the  hand 
lever  there  will  thus  be  some  position  of  the  piston, 
rock  shaft  arm  and  main  valve  gear,  for  which  the  valve  will  be 
brought  to  mid  position  and  the  piston  and  gear  thus  brought  to 
rest,  and  that  the  steam  will  carry  the  gear  to  this  position  and 
then  automatically  shut  off  and  stop.  If  the  hand  lever  is  moved 
but  slightly  so  as  to  barely  displace  the  valve,  the  piston  will 
move  but  a  small  distance  before  again  covering  the  ports  antl 
coming  to  rest.  If  the  handle  be  moved  to  an  extreme  position 
the  valve  will  be  moved  far  over  and  the  steam  will  rush  the 
piston  and  gear  over  into  the  extreme  corresponding  position. 
In  short,  the  position  of  the  gear  for  equilibrium  under  steam  will 
correspond  exactly  to  that  of  the  hand  lever,  and  wherever  the 
latter  may  be  placed,  the  gear  will  run  to  the  corresponding 
position  and  then  stop.  It  is  also  clear  that  if  the  hand  lever  be 
moved  slowly,  the  piston  and  main  links  will  follow  along  at 
equal  pace,  stopping  when  the  handle  is  stopped  and  moving 
when  it  moves.  Also  if  the  handle  be  slightly  displaced  and  left 
to  itself  the  friction  of  moving  the  valve  will  be  usually  more 
than  that  of  moving  the  handle,  and  in  consequence  the  point,  I, 
will  become  for  the  time  a  fixed  center,  and  the  piston  will  move 
along,  the  valve  remaining  open  and  the  connection,  HKN, 
moving  the  handle  over  at  equal  pace  with  the  link.  This  will 
continue  till  the  handle  comes  against  a  stop  at  the  end  of  its 
path.  The  point,  K,  will  then  become  fixed,  and  the  further 
movement  of  the  piston  will  move  the  valve  into  mid-position, 


MARINE  ENGINES.  .  219 

thus  shutting  off  steam  and  bringing  the  gear  to  rest  in  the 
position  corresponding  to  that  of  the  hand  lever. 

To  take  up  sudden  shocks  and  provide  a  safeguard  against 
putting  the  link  over  too  rapidly  and  thus  overrunning  at  the  end 
through  the  inertia  of  the  parts,  spring  stops  or  buffers,  R,  are 
provided  on  a  rod,  S,  against  which  the  lug,  Q,  comes  at  the 

end  of  its  run. 

» 

It  is  thus  seen  that  this  gear  furnishes  a  very  perfect  con- 
trol over  the  main  valve  gear,  the  action  being  the  same  as  for  a 
man  operating  the  gear  directly,  and  thus  giving  him  readiness 
of  control  with  the  least  mental  effort,  and  the  least  liability  of 
error  in  a  moment  of  hurry  or  excitement. 

In  addition  to  the  spring  buffers,  as  shown  in  Fig.  169,  a 
form  of  plunger  control  is  sometimes  added.  In  this  arrange- 
ment the  piston  rod  of  the  reverse  cylinder  is  continued  back- 
ward and  connected  to  a  second  piston  or  plunger  working  in  a 
cylinder  filled  with  oil.  The  operation  of  the  plunger  is  to  trans- 
fer the  oil  through  a  suitable  pipe  connection  from  one  end  of 
the  cylinder  to  the  other,  and  as  this  passage  may  be  throttled 
at  will  by  a  stop  valve,  all  possibility  of  slamming  or  of  violent 
motion  may  be  removed.  A  further  advantage  of  this  arrange- 
ment lies  in  the  fact  that  with  suitable  pipe  connections  to  a 
hand  pump,  the  oil  may  be  drawn  from  one  side  of  the  plunger 
and  forced  in  on  the  other,  thus  giving  a  control  over  the  valve 
gear  by  hand  power  in  case  of  derangement  of  the  power  con- 
trol. 

Of  other  forms  of  reverse  gear  the  so-called  all  around  gear 
is  quite  commonly  met  with  in  English  practice.  The  main 
links  are  connected  up  to  a  small  engine  which  makes  a  large 
number  of  revolutions  in  running  the  link  over  from  one  extreme 
to  the  other.  This  engine  is  under  the  control  of  a  small  link 
which  is  directly  operated  by  hand.  A  form  of  lever  stop  is 
usually  provided  which  will  either  reverse  or  middle  the  small 
link  and  bring  the  engine  to  rest  when  the  main  links  have 
reached  either  extreme  of  their  travel. 

In  engines  for  small  yachts,  launches,  etc.,  the  links  are 
placed  directly  under  the  control  of  a  hand  lever. 

The  various  other  types  of  valve  gear  may  be  operated  by 
any  of  the  forms  of  reverse  described.  With  all  valve  gears,  as 
described  in  Chapter  VII,  the  reverse  is  effected  by  the  move- 
ment of  some  piece  of  the  gear  from  one  position  or  location  into 


220  PRACTICAL  MARINE  ENGINEERING. 

another,  and  so  back  and  forth  for  the  various  degrees  of  linking 
up,  etc.  By  suitably  connecting  such  piece  to  the  power  re- 
verse gear  the  control  may,  therefore,  be  obtained  in  the  same 
manner  as  for  the  Stephenson  link  as  described  above. 

[6]  Turning  Gear. 

It  is  always  necessary  to  provide  some  means  for  turning 
the  engine  other  than  by  steam  on  the  main  pistons.  This  is 
necessary  for  moving  the  engine  when  in  port  for  adjustment  of 
bearings,  setting  of  valves,  etc.  The  turning  gear  usually  con- 
sists of  a  large  worm  wheel  placed  on  the  main  shaft  just  aft  of 
the  bed-plate,  geared  down  through  worm  and  spur  gearing  to  a 
small  engine,  usually  a  double  simple  engine  with  cranks  at  90°. 
The  gearing  ratio  is  such  that  many  hundred  revolutions  of  the 
turning  engine  may  be  required  to  one  of  the  turning 
wheel  or  main  engine  shaft.  This  gear  must  be  so  ar- 
ranged as  to  be  readily  thrown  in  and  out  of  connection  with 
the  main  turning  wheel.  This  is  usually  accomplished  by  carry- 
ing the  main  worm  on  a  shaft  which  is  pivoted,  and  which  can 
thus  be  locked  in  either  of  two  positions,  in  one  of  which  the 
worm  is  in  gear,  and  in  the  other  out  of  gear,  or  else  by  driving 
the  worm  on  a  shaft  with  a  feather,  thus  providing  for  endwise 
motion,  and  for  fixing  it  in  either  of  two  locations  on  its  shaft, 
in  one  of  which  it  is  in  gear  and  in  the  other  out  of  gear.  The 
latter  is  the  arrangement  more  commonly  met  with. 

Where  a  turning  engine  is  not  provided  the  turning  wheel 
is  usually  arranged  for  operation  by  hand  through  worm  gear- 
ing operated  by  a  lever  with  pawl  and  ratchet  arrangement,  or 
by  some  similar  device. 

In  some  cases  the  engine  is  turned  by  a  hydraulic  jack 
placed  under  a  movable  chock  piece  located  in  sockets  cast  in 
the  turning  wheel.  This  chock  is  shifted  from  one  socket  to  an- 
other as  the  jack  shoves  it  upward,  and  thus  the  engine  is  slowly 
turned. 

In  small  engines  the  turning  wheel  is  often  simply  a  form  of 
gear  wheel  with  shallow  teeth  in  which  a  pinch  bar  is  worked, 
and  by  this  means  the  engine  may  be  slowly  pried  around.  Such 
a  wheel  is  known  as  a  pinch  wheel. 

[7]  Joints  and  Packing. 

The  joints  to  be  considered  under  this  head  are  of  two 
kinds,  (i)  Fixed  joints  as  those  between  a  cylinder  or  valve 


MARINE  ENGINES.  221 

chest  cover  and  flange,  and  (2)  Sliding  or  slip  joints  as  those  be- 
tween a  piston  rod  and  the  stuffing  box,  or  the  slip  joint  in  a 
length  of  steam  piping. 

For  making  up  stationary  joints  a  great  variety  of  packings 
are  in  use,  the  difference  depending  to  some  extent  upon  the 
temperature  to  which  the  joint  is  to  be  subjected.  Thus 
for  joints  to  stand  high  temperature,  as  with  boiler  man- 
holes, cylinder  heads,  etc.,  sheet  asbestos  either  plain  or 
in  combination  with  other  materials  is  used.  There  are 
also  various  kinds  of  packing  in  which  rubber  in  one  form 
or  another  is  used  either  in  combination  with  some  fibrous  ma- 
terial as  sheet  canvas,  or  as  a  constituent  of  some  form 
of  compound.  The  tendency  of  rubber  by  itself  is  to  grow 
dry,  hard  and  brittle,  especially  under  the  action  of  heat,  and  the 
purpose  of  the  modern  forms  of  rubber  compound  is  to  avoid 
this  tendency,  at  the  same  time  retaining  its  elasticity  and  joint 
making  qualities.  For  joints  not  subject  to  the  action  of  high 
temperature,  similar  forms  of  packing  are  used,  though  with  a 
greater  proportion  of  rubber,  if  desired. 

The  strip  or  ring  of  packing  which  is  cut  out  and  fitted 
for  the  joint  is  called  a  gasket. 

In  making  up  such  a  joint  it  is  well  to  smear  the  surfaces 
of  the  gasket  with  a  mixture  of  black-lead  and  grease  or  oil. 
This  will  aid  somewhat  in  making  the  joint,  and  very  much  in 
the  removal  of  the  cover  and  gasket  at  a  later  time  without  tear- 
ing the  latter.  With  such  precaution  and  when  the  temperature 
is  not  high  the  same  gasket  may  be  used  several  times  over  with- 
out loss  of  its  joint  making  qualities. 

In  addition  to  gaskets  made  of  such  materials  as  described 
above,  joints  are  also  made  with  gaskets  of  corrugated  sheet 
copper,  or  of  plain  copper  wire.  For  high  pressures  such  gas- 
kets have  proved  quite  successful.  The  soft  copper  is  expanded 
between  the  harder  metals  of  the  flanges,  and  spreads,  filling  the 
surfaces  where  it  touches,  thus  making  a  tight  joint. 

For  sliding  joints  as  between  a  piston-rod  and  stuffing-box, 
the  greatest  variety  of  packings  is  likewise  in  use.  They  may 
be  broadly  divided,  however,  into  the  two  classes,  fibrous  and 
metallic. 

The  fibrous  packings  are  made  of  the  same  material  as  the 
sheet  packings  above  described,  and  are  either  round,  square  or 
triangular  in  section.  For  use.  they  are  cut  to  such  lengths  as 


222 


PRACTICAL  MARINE  ENGINEERING. 


may  be  necessary  and  placed  in  the  stuffing-box  in  layers  or 
turns,  the  joints  between  the  ends  being  shifted  so  as  not  to 
come  one  above  another.  The  stuffing-box,  as  shown  in  section 
in  Fig.  170,  consists  of  a  cylindrical  chamber  or  box,  EF,  with 
cavity  B.  This  is  bolted  by  means  of  the  flange,  F,  to  the  lower 
cylinder  head.  The  part,  CC,  is  known  as  the  gland  or  follower 
and  is  carried  by  two  or  more  studs,  as  shown.  At  the  bottom 
or  upper  end  of  the  box  is  a  ring,  as  shown,  just  filling  in  the 
space  between  the  opening  in  the  box  and  the  piston  rod.  Fre- 


Fig.  170.     Plain  Stuffing  Box. 

quently  this  ring  is  omitted  and  the  metal  of  the  box  fits  about 
the  rod.  The  packing  is  placed  in  the  box  as  described  above, 
thus  filling  the  space,  BB,  between  the  bottom  of  the  box 
and  the  gland.  The  packing  may  then  be  compressed  as  de- 
sired and  as  may  be  necessary  by  means  of  the  nuts  on  the  stud- 
bolts,  thus  forcing  the  gland  down  on  the  packing  and  making 
the  joint  tight.  This  is  the  general  type  of  all  such  joints  made 
with  compressible  packing,  with,  of  course,  variation  in  details. 
Joints  of  this  character  are  used  for  piston  and  plunger 


MARINE  ENGINES. 


223 


rods,  slide  valve  stems,  globe  and  disc  valve-stems,  joints  about 
the  shaft  where  it  goes  through  a  water-tight  bulkhead,  joint  in 
the  thrust  bearing  casing,  as  noted  in  section  21  [n],  in  slip  and 
expansion  joints,  as  noted  in  section  25  [2],  etc.,  etc. 

For  metallic  packing  with  joints  of  this  character  the  form 
of  the  box  is  in  general  the  same.  In  fact  in  some  cases  the 
box  is  so  made  that  either  soft  or  metallic  packing  may  be  used. 
Here  again  the  greatest  variety  in  detail  is  to  be  found,  but  a 


Fig.  171.     Metallic  Packing. 

single  instance  will  serve  to  illustrate  the  essential  features  of 
such  packing. 

In  Fig.  171  is  shown  an  example  of  metallic  packing.  The 
box  or  casing  contains  at  its  bottom,  or  upper  end  in  the 
cut,  a  spiral  spring,  as  shown.  Next  comes  a  brass  ring,  and 
next  a  series  of  babbitt  or  white  metal  rings  carried  in  a  casing 
or  shell,  as  shown.  These  rings  are  conical  on  the  outer  cir- 
cumference, and  fit  to  a  corresponding  form  of  the  containing 


224  PRACTICAL  MARINE  ENGINEERING. 

shell.  Next  below  is  a  second  brass  ring  which  supports  the 
shell  above,  the  joint  between  the  two  being  ground  to  a  tight 
fit.  This  ring  rests  on  a  casing  below,  the  joint  between  the 
two  being  spherical  and  ground  to  a  fit.  The  latter  cas- 
ing contains  another  spiral  spring  and  then  follows 
another  series  of  rings,  etc.,  similar  to  those  above.  The 
whole  box  contains,  therefore,  two  similar  sets  of  packing  ele- 
ments, each  consisting  of  a  spiral  spring,  white  metal  rings  con- 
taining shell,  etc.  Each  of  the  white  metal  rings  consists  of  two 
separate  halves,  the  whole  arranged  so  as  to  break  joints  from 
one  ring  to  the  next.  It  is  readily  seen  that  the  action  of  the 
spring  is  to  crowd  the  white  metal  packing  rings  into  the  conical 
shell  and  hence  against  the  rod,  thus  keeping  the  joint  tight  be- 
tween the  two.  It  is  further  seen  that  with  this  way  of  carrying 
the  packing  the  latter  is  entirely  unconstrained  laterally,  and 
may  move  in  any  way  to  accommodate  itself  to  any  slight  ir- 
regularity in  the  rod  without  danger  of  disturbing  the  tight- 
ness of  the  joint.  The  two  systems  of  packing,  as  a  whole,  are 
held  up  into  place  by  an  outer  ring,  secured  to  the  cylinder  head 
by  stud  bolts.  The  joint  between  the  packing  systems  and  the 
cylinder  is  made  by  a  ring  of  copper  wire,  as  shown,  thus  shut- 
ting off  all  leakage  of  steam  from  the  packing  space  in  this  di- 
rection, while  the  various  ground  joints  and  packing  ring  sur- 
faces close  it  off  in  other  directions. 

Among  the  various  conditions  which  an  ideal  packing  for 
piston  and  valve  rods  should  fulfil  those  of  chief  importance  may 
be  stated  as  follows : 

(1)  The  packing  should  make  a  steam  tight  joint  between 
rod  and  stuffing  box,  at  the  same  time  opposing  the  minimum 
frictional  resistance  to  the  motion  of  the  former. 

(2)  It  must  be  durable   even   under  the  temperature   of 
modern  high  pressure  steam,  and  also  easily  removed  or  replaced 
with  new  when  necessary. 

(3)  The  packing  should  be  free  to  move  about  transverse- 
ly to  a  sufficient  extent  to  follow  the  rod,  even  if  it  is  slightly 
bent  or  out  of  line,  at  the  same  time  maintaining  the  joints  steam 
tight  between  the  rod  and  the  packing,  and  between  the  packing 
and  the  stuffing-box. 

Requirement  (3)  has  given  the  greatest  trouble  and  has  led 
to  many  varieties  of  design  intended  to  cover  the  point,  one  of 
which  is  illustrated  as  above  in  Fig.  171.  No  packing  can  be 


MARINE  ENGINES.  225 

considered  satisfactory  for  modern  requirements  which  does  not 
possess  in  good  degree  the  qualities  detailed  above. 

[8]  Reheaters. 

A  reheater  is  a  collection  of  pipes  placed  in  a  receiver  or  ex- 
haust passage  from  one  cylinder  to  the  next.  Within  these  pipes 
high  pressure  steam  is  circulated,  and  around  them  the  exhaust 
steam  passes.  The  high  pressure  steam  will,  therefore,  give  up 
its  heat  to  the  cooler  exhaust  steam,  and  thus  tend  to  dry  or 
even  to  superheat  it  as  it  passes  on  into  the  next  cylinder 
beyond.  The  office  of  the  reheater  is,  therefore,  to  exercise  a 
drying  and  heating  action  on  the  exhaust  steam  as  it  passes 
from  one  cylinder  to  another  in  a  multiple  expansion  engine. 
Under  most  conditions  this  will  exert  a  beneficial  influence  on 
the  economy  of  the  engine  by  decreasing  the  amount  of  cylinder 
condensation,  and  to  such  action  may  be  referred  the  benefit 
which  the  reheater  seems  to  give.  See  further  Section  59. 

[9]  Governors. 

In  order  to  control  the  revolutions  of  the  engine  and  to 
prevent  violent  increasing  or  racing  when  the  propeller  is  par- 
tially lifted  out  of  the  water  by  the  pitching  of  the  ship,  some 
form  of  governor  is  frequently  fitted.  The  early  types  of  mar- 
ine engine  were  usually  governed  by  hand  at  the  throttle,  which 
was  commonly  of  the  butterfly  variety  (see  Section  24  [i]), 
though  occasionally  automatic  means  of  moving  the  valve  were 
employed.  With  modern  multiple  expansion  engines,  however, 
it  is  impossible  to  satisfactorily  control  the  revolutions  by  the 
throttle.  With  such  engines  the  control  must  come  from  the 
slide  valve  gear,  the  links  of  which  may  be  linked  up  more  or 
less,  as  required  when  the  propeller  is  uncovered,  and  linked  out 
again  as  it  is  submerged.  Where  no  automatic  governor  is 
fitted,  this  must  be  done  by  hand  control  of  the  reversing  gear. 
The  modern  automatic  governor  is  intended  to  take  the  place 
of  this  hand  control. 

There  are  two  modes  of  actuating  marine  governors. 

(1)  By  utilizing  the  varying  pressure  under  the  stern. 

(2)  By  utilizing  a  variation  in  the  revolutions  from  the  reg- 
ular speed. 

In  the  first  type  a  pipe  is  run  from  the  outside  water  at  the 
stern  to  some  form  of  pressure  chamber  near  the  engine,  within 
which  is  a  flexible  diaphragm  held  in  position  by  a  spring  or 


226  PRACTICAL  MARINE  ENGINEERING. 

other  equivalent  means.  The  water  being  admitted  to  this  pipe, 
the  air  within  is  compressed  according  to  the  head  of  water  over 
the  outer  end.  The  apparatus  is  so  adjusted  that  at  normal  draft 
the  diaphragm  is  in  equilibrium  between  the  two  forces,  due  to 
the  water  pressure  on  the  one  side  and  the  spring  on  the 
other.  A  change  in  the  depth  of  the  water  will  cause  a  varia- 
tion in  the  pressure  which  will  be  transmitted  through  the  air 
and  thus  destroy  the  equilibrium,  throwing  the  diaphragm  in 
one  direction  or  the  other.  This  may  be  made  to  actuate  a 
steam  valve  and  thus  through  an  auxiliary  steam  piston  control 
the  reversing  lever  and  through  this  the  links.  In  former 
practice  this  type  of  gear  was  sometimes  made  sufficiently  large 
to  actuate  the  steam  throttle  directly,  or  sometimes  a  like  valve 
in  the  exhaust  pipe. 

The  other  type  of  governor  is  found  in  various  forms.  In 
many  of  them  use  is  made  of  the  centrifugal  force  of  revolving 
balls  or  weights  somewhat  as  in  the  ordinary  stationary  gover- 
nor. Through  the  force  thus  available  a  small  valve  is  oper- 
ated, thus  leading  through  a  series  of  steps  to  the  control  of  the 
reverse  lever  or  other  part  which  it  is  desired  to  operate.  Again 
in  other  forms  a  revolving  fan  or  propeller  working  in  a  box 
filled  with  liquid  maintains  the  apparatus  in  a  certain  condition 
at  a  certain  speed.  With  a  sudden  change  of  speed  a  corre- 
sponding change  of  resistance  to  the  motion  is  met  with,  and  this 
difference  of  force  may  be  used  to  operate  a  small  valve,  and 
then,  as  before  through  the  proper  steps,  the  reversing  lever  is 
controlled.  In  another  form  a  pump  continually  forces  air  into 
a  chamber  from  which  it  escapes  through  a  cock  whose  opening 
may  be  regulated  at  will.  For  a  given  size  of  outlet  and  speed 
of  pump  the  pressure  will  rise  until  finally  as  much  escapes  as 
enters  and  the  pressure  remains  constant.  If  the  speed  changes, 
however,  the  pressure  will  change  correspondingly,  and  this 
difference  of  pressure  will  give  a  force  which  may  be  used  as 
already  explained. 

A  still  different  type  of  gear  operated  by  a  change  of  speed 
but  not  driven  by  the  use  of  a  belt  employs  the  forces  due  to 
inertia.  As  usually  installed  it  consists  of  a  weighted  vertical 
rod  pivoted  at  the  top  so  that  if  unrestrained  it  could  swing  to 
and  fro  between  a  pair  of  stops.  This  weight  with  its  point  of 
suspension  is  then  given  a  movement  of  reciprocation  horizon- 
tally by  attachment  to  any  suitable  part  of  the  engine.  If  not 


MARINE  ENGINES.  227 

prevented,  it  would  therefore  swing  to  and  fro  between  the 
stops,  due  to  the  change  in  momentum  imparted  by  the  re- 
ciprocating motion.  It  is,  however,  held  by  a  spring  against  one 
of  the  stops,  and  the  tension  is  so  adjusted  that  movement  will 
not  result  until  the  engine  exceeds  its  normal  speed,  when  the 
inertia  forces  overcome  the  spring,  and  the  weight  moves  away 
from  the  stop.  This  motion,  by  means  of  an  attached  lever,  may 
operate  an  auxiliary  valve,  piston,  etc.,  and  thus  control  the 
links.  This  type  of  governor  is  sometimes  used  only  as  a  safety 
gear  to  quickly  stop  the  engine  in  case  of  a  breakage  of  the  shaft 
or  other  accident  permitting  violent  racing.  In  such  case  the 
gear  is  sometimes  so  arranged  that  the  movement  of  the  weight 
away  from  the  stop  will  cause  it  to  engage  as  a  clutch  with  an 
arm  or  lever  connected  with  the  reverse  lever,  and  so  adjusted 
that  the  motion  given  will  just  bring  the  links  to  the  mid  posi- 
tion. The  instant  the  weight  leaves  the  stop,  therefore,  the 
levers  will  be  suddenly  thrown  over,  the  links  middled  and  the 
engine  stopped. 

All  forms  of  marine  governor  are  somewhat  slow  in  control- 
ling the  variations  of  speed.  The  ideal  governor  would  antici- 
pate the  motion  and  close  down  or  open  up  just  in  advance  of 
the  rise  in  speed.  Instead  of  this  they  act  only  after  the  stern  has 
risen  or  fallen,  or  after  the  change  of  speed  has  become  more 
or  less  pronounced.  It  is  considered  good  practice,  however, 
to  fit  some  form  of  governor,  at  least  as  an  emergency  control, 
so  as  to  prevent  an  excessive  increase  of  revolutions  from  any 
cause  whatever.  For  this  purpose  only  those  forms  which  de- 
pend on  a  change  of  speed  are  suitable,  and  such  are  commonly 
fitted  in  modern  practice. 

[10]  Counter  Gear. 

The  revolutions  of  the  engine  are  automatically  registered 
by  a  counter  of  the  common  type,  and  consisting  of  a  series  of 
discs  with  numbers  from  o  to  9  on  their  circumferences.  The 
motion  for  the  counter  is  taken  from  any  reciprocating  piece 
which  has  a  convenient  location  and  a  motion  of  small  range. 
This  is  connected  up  to  the  counter  by  appropriate  links,  bell 
cranks,  etc.  The  motion  operates  directly  on  the  disc  to  the 
right  and  moves  it  along  one  notch  or  figure  for  each  revolution. 
As  each  disc  reaches  o  it  engages  with  the  one  of  next  higher 
order  on  the  left  and  throws  it  over,  thus  carrying  the  count 
continuously  along  the  discs  from  the  first  to  the  last. 


228  PRACTICAL  MARINE  ENGINEERING. 

In  this  way  the  revolutions  are  registered  one  by  one,  the 
total  number  for  any  period  of  time  being  found  by  taking  the 
difference  of  the  two  readings  for  the  beginning  and  end  of  this 
period.  By  this  means  the  revolutions  per  minute,  per  hour  or 
per  day  are  readily  found  as  desired. 

(n]   Lagging. 

The  cylinders,  cylinder-heads,  valve  chests  and  covers  are 
usually  provided  with  some  form  of  covering  intended  to  prevent 
the  loss  of  heat,  and  thus  conduce  to  economy  as  well  as  render 
the  engine  less  disagreeable  to  work  near  and  about.  Such 
covering  is  known  as  lagging  and  consists  usually  of  either  wood 
in  strips  or  polished  sheet  brass  or  Russia  iron.  When  of  wood 
the  strips  are  narrow,  I  to  2  inches  in  width,  and  often  of  alter- 
nate light  and  dark  color  to  give  a  pleasing  effect.  They  are 
usually  matched  together  and  secured  by  bands  of  brass  or  pol- 
ished iron,  or  by  brass  headed  screws  taking  into  foundation 
pieces  held  in  place  by  countersunk  tap  bolts. 

[12]  Lubrication  and  Oiling  Gear. 

(i)  Lubricants.  For  the  lubrication  of  the  various  rubbing 
surfaces  and  turning  joints,  except  within  the  cylinder,  olive  oil, 
castor  oil,  and  the  lubricating  grades  of  mineral  oil  are  used. 
Olive  oil  when  pure  is  a  most  excellent  lubricant,  especially  for 
machinery  of  moderate  or  light  weight,  but  it  is  liable  to  adul- 
teration by  peanut  oil  or  other  oils  of  an  inferior  quality.  For 
the  lubrication  of  the  internal  surfaces  nothing  but  the  best  min- 
eral oil  must  be  used.  (See  Sec.  40.)  The  grade  commonly 
employed  is  known  as  cylinder  oil,  and  is  heavy  and  viscid  at 
ordinary  temperatures,  becoming  quite  fluid,  however,  at  the 
usual  temperatures  of  the  steam.  It  is  usually  fed  in  by  means 
of  a  sight  feed  lubricator,  as  described  in  (9). 

In  addition  to  the  liquid  oils,  various  lubricating  greases  are 
used,  often  in  combination  with  a  certain  proportion  of  graphite 
(black  lead.)  Graphite  alone  or  in  combination  with  oil 
is  also  used,  and  its  lubricating  qualities  are  of  the  highest 
order.  It  seems  to  possess  the  property,  especially  with  cast 
iron,  of  filling  the  pores  of  the  iron,  and  of  thus  forming  a  kind 
of  graphite-metal  skin  on  the  surface,  with  a  very  small  co- 
efficient of  friction. 

The  place  where  the  lubricant  should  be  supplied  to  the 
bearing  is  a  subject  which  has  attracted  considerable  attention 


MARINE  ENGINES.  229 

in  the  past  few  years.     It  seems  now  to  be  very  well  established 
that  the  following  principles  should  govern : 

(a)  The  oil  should  always,  where  possible,  be  led  into  the 
bearing  at  a  point  which  is  under  the  smallest  pressure. 

(b)  The  continuity  of  the  oil  film,  where  it  is  under  the 
greatest  pressure,  should  not  be  interrupted  by  oil  channels  or 
grooves. 

(c)  The  oil  should  be  prevented,  as  far  as  possible,  from 
escaping  at  those  points  which  are  under  the  greatest  pressure. 

For  journals  such  as  main  pillow-blocks,  etc.,  these  princi- 
ples are  very  commonly  violated,  and  in  fact  it  can  hardly  be 
said  that  practice  has  as  yet  come  to  act  upon  them,  though  their 
correctness  seems  to  have  been  well  demonstrated.  According 
to  these  principles  the  oil  for  the  main  pillow  block  bearings 
should  be  introduced  near  the  division  between  the  upper  and 
lower  brasses,  and  the  oil  scores  or  grooves  in  the  metal  of  the 
bearing  at  the  top  and  bottom  should  be  omitted.  Similarly  for 
the  crank-pin  and  other  cylindrical  journals,  the  oil  should  be 
admitted  at  those  points  where  there  is  the  least  pressure,  and 
at  the  points  where  the  pressure  is  greatest  the  bearing  surface 
should  be  smooth  and  not  interrupted  by  grooves,  or  scores,  or 
oil  channels  of  any  kind  whatever. 

(2)  Amount  of  Lubricant  Required..  As  to  the  amount  of  oil 
to  be  used,  practice  differs  widely,  but  from  5  to  8  Ib.  of  oil  per 
ton  of  coal  may  be  taken  as  a  fair  allowance,  or  say  from  5  to  8 
Ib.  per  looo  I.  H.  P.  per  hour.  In  small  sizes,  for  engines  of  the 
torpedo  boat  type,  etc.,  the  consumption  will  go  up  to  consider- 
ably larger  figures.  Of  this  total  amount  some  5  to  10  per  cent, 
may  be  required  for  internal  lubrication,  and  the  remainder  for 
the  various  joints,  bearings,  etc. 

In  the  opinion  of  many  good  engineers,  after  a  ship  has 
been  at  sea  for  a  few  days  and  the  machinery  has  settled  into  a 
steady  running  condition,  the  amount  of  internal  lubricant  may 
be  gradually  decreased  to  perhaps  one-half  the  amount  first 
used. 

With  regard  to  the  frequency  of  lubrication  no  definite  rules 
can  be  given.  The  ideal  system  is,  of  course,  as  nearly  con- 
tinuous as  possible.  Where,  however,  the  continuous  system  is 
not  in  use  and  intermittent  oiling  must  be  depended  on,  the  vari- 
ous joints  and  stuffing  boxes  will  require  attention  and  a  fresh 
supply  of  lubricant  at  intervals  of  from  perhaps  twenty  minutes 


230  PRACTICAL  MARINE  ENGINEERING. 

to  one  hour.  For  the  various  pin  and  turning  joints,  main 
guides,  etc.,  the  lubricant  is  usually  supplied  by  oil  cups  or  cans 
of  character  suited  to  the  particular  use  for  which  intended, 
while  the  piston  and  valve  rods  are  lubricated  by  means  of  a 
swab  charged  with  cylinder  oil  or  special  grease.  The  main 
guides  are  also  in  some  cases  lubricated  by  the  swab  rather  than 
the  can. 

There  is  also  a  growing  tendency  in  engines  of  the  high 
speed  type  as  used  on  torpedo  boats,  etc.,  and  where  the  steam 
is  always  more  or  less  moist,  to  depend  on  water  lubrication, 
and  to  avoid,  so  far  as  possible,  the  use  of  internal  lubricant. 
This  end  may  be  furthered  by  careful  workmanship  in  the  fitting 
up  of  valves  and  pistons,  and  by  driving  the  engine  by  belt  or 
otherwise  in  the  erecting  shop  with  the  surfaces  charged  with 
graphite.  The  minute  pores  of  the  metal  are  thus  filled  with  the 
graphite,  and  rubbing  surfaces  are  developed  which  run  very 
well  without  further  lubrication. 

(3)  Adjustment  of  Bearings.     For  a  bearing  in  good  adjust- 
ment the  clearance  or  distance  between  the  journal  and  bearing 
surface  is  proportioned  to  the  size  of  the  journal,  and  may  be 
made  about  .002  or  1-5  of  i  per  cent,  of  the  diameter.     With  a 
lubricant  of  proper  consistency  and  a  load  per  square  inch  not 
too  great,  say  not  over  400  to  500  Ib.  per  square  inch  of  project- 
ed area,  the  film  of  oil  will  retain  its  place,  and  insure  the  proper 
lubrication  of  the  bearing.      If  too  thin  a  lubricant  is  used  the 
bearing  may  heat  and  pound  simply  because  the  journal  is  not 
supported  by  the  film  of  oil.     The  proper  consistency  of  the  oil 
as  influenced  by  its  natural  viscosity  and  by  the  temperature  of 
the  bearing  may,  therefore,  determine  to  a  considerable  extent 
the  smooth  running  or  pounding  of  the  various  joints  and  jour- 
nals. 

DEVICES  EMPLOYED  FOR  SUPPLYING  LUBRICANT 
TO  BEARINGS. 

We  will  now  describe  the  more  important  devices  for  sup- 
plying oil  and  grease  to  the  bearings,  or  to  the  points  where  re- 
quired. 

(4)  Wick  Cup.    The  plain  wick  cup  consists  of  a  receptacle, 
usually  of  cast  brass,  fitted  with  a  cover,  and  placed  at  a  conven- 
ient point  for  the  delivery  of  the  oil  to  the  bearing.      It  is  also 
frequently  formed  as  a  part  of  the  bearing  cap,  as  in  Fig.  147. 


MARINE  ENGINES 


231 


A  tube,  as  shown,  enters  through  the  bottom  of  the  oil  reservoir 
and  rises  within  to  a  point  above  the  level  at  which  it  is  expected 
to  carry  the  oil.  This  tube  leads  downward  to  the  duct  which 
carries  the  oil  to  the  point  of  delivery  to  the  bearing.  The 
"wick"  consists  of  a  few  threads  of  cotton  wicking,  one  end  of 
which  is  wrapped  with  a  bit  of  wire,  which  then  serves  as  a 
handle  for  pushing  it  down  the  tube  or  for  pulling  it  out.  In  op- 
eration, one  end  of  the  wick  is  pushed  down  the  tube  and  the 
other  end  dipped  in  the  oil.  Through  the  action  of  capillary  at- 
traction the  oil  rises  in  the  wick  on  the  outside,  and  then  by  a 
combination  of  capillary  and  siphon  action  descends  and  drips 
down  the  tube  to  the  bearing.  The  end  of  the  wick  within  the 
tube  should  be  pushed  down  below  the  level  of  the  bottom  of  the 
cup  so  that  this  shall  form  the  longer  leg  of  the  siphon. 

The  size  of  the  wick  should  be  adjusted  according  to  the 
amount  of  oil  which  it  is  desired  to  feed  and  to  the  quality  of  the 
oil  as  well.  This  adjustment  of  size  is  most  easily  effected  by 
varying  the  number  of  strands  of  cotton  in  the  wick.  The 


Fig.  172.     Wiper. 


Fig  .173.     Oil  Cup  with  Adjustable  Feed. 


amount  fed  may  also  be  varied  to  some  extent  by  regulating  the 
distance  to  which  the  wick  is  pushed  down  the  inner  tube. 

For  a  sudden  flush  of  oil  the  cups  may  be  filled  until  they 
overflow  into  the  inner  tube,  by  which  means  the  bearing  may 
be  flooded  if  desired. 

(5)  Wiper.     A  wiper  is  shown  in  Fig.  172.      It  consists  of 


232 


PRACTICAL  MARINE  ENGINEERING. 


an  oil  cup  with  a  central  blade  or  plate,  A,  extending  above  the 
edge,  and  attached  to  one  of  the  moving  parts  of  the  engine.  At 
a  convenient  point  is  placed  a  strip  of  fibrous  material  on  to 
which  the  oil  is  fed  from  the  source  of  supply.  The  strip  and 
wiper  are  so  adjusted  that  the  latter  in  its  motion  to  and  fro 
wipes  or  scrapes  along  the  lower  surface  of  the  former,  and  thus 
as  soon  as  the  strip  is  saturated  with  oil  the  wiper  takes  off  a 
drop  or  more  which  then  runs  down  into. the  cup  and  thence  to 
the  surfaces  to  be  lubricated.  Naturally  this  mode  of  lubrica- 
tion is  more  especially  suited  to  parts  having  a  horizontal  mo- 
tion. 


Fig.   174. 


Marine  Engineering 

Oil   Cup  with   Screw   Cover. 


Marine  Engineering 

Fig.   175.     Oil   Cup  with   Sight  Feed. 


(6)  Plain  Oil  Cup  With  Adjustable  Feed.  This  consists  of  a 
simple  cup,  as  shown  in  Fig.  173,  mounted  where  convenient 
and  connected  by  pipe  or  duct  to  the  bearing  to  be  supplied. 
The  rate  of  feed  is  regulated  by  a  needle  or  conical  valve,  which 
controls  the  size  of  opening  through  the  discharge  passage  in 
the  base.  A  cover  is  usually  fitted  to  prevent  spilling  or  the  ad- 
mission of  impurities.  Where  such  a  form  of  cup  is  used  to  ad- 
mit oil  to  a  steam  chest  or  other  chamber  under  pressure,  a 
strong  screw  cover  is  necessary,  as  shown  in  Fig.  174.  To  fill 
the  cup  in  such  case  the  valve  is  closed,  the  cover  unscrewed,  and 


MARINE  ENGINES.  233 

the  cup  filled.  The  cover  is  then  replaced  and  the  valve  opened 
according  to  the  rate  of  feed  desired.  ^  Another  variety  of  cup 
used  for  this  purpose  has  a  body  of  cylindrical  or  globular  form 
terminating  at  top  and  bottom  in  a  neck  or  tube,  each  of  the 
latter  being  closed  by  a  valve.  The  lower  neck  joins  the  tube 
leading  to  the  bearing  as  in  other  cups,  while  to  the  upper  is 
fixed  a  shallow  open  cup.  The  chamber  between  the  two 
valves  is  filled  by  closing  the  lower  valve,  opening  the  upper 
and  pouring  into  the  shallow  cup  which  serves  thus  simply  as  a 
funnel.  When  filled,  the  upper  valve  is  closed  and  the  lower  one 
opened  according  to  the  rate  of  feed  desired. 

(7)  Sight  Feed  Oil  Cup.     As  shown  in  Fig.  175,  this  is  es- 
sentially a  plain  cup  with  the  addition  of  the  "sight-feed"  attach- 
ment or  feature.     When  in  adjustment,  the  flow  of  oil  is  regu- 
lated by  the  conical  valve  to  a  drop  at  a  time  at  such  interval 
as  may  be  desired.     The  space  below  the  outlet  of  the  cup  is 
cut  away  so  as  to  show  the  drop  as  it  falls  into  the  mouth  of  the 
feeding  tube.     Very  frequently  a  glass  tube  is  fitted  inside  the 
brass  framework,  thus  closing  in  the  oil  completely,  but  allowing 
the  drop  to  be  seen  as  it  falls. 

For  a  sudden  flush  of  oil  it  is  only  necessary  to  open  up  the 
conical  valve  sufficient  to  let  the  oil  descend  in  a  stream  and 
flood  the  bearing. 

(8)  Compression  Grease  Cup.     In  addition  to  oil,  various 
forms  of  hard  grease  in  cakes,  or  balls,  or  in  bulk,  are  some- 
times used  for  lubricating  purposes.      For  feeding  such  lubri- 
cating material  to  bearings  two  means  are  made  use  of. 

(i)  If  the  bearing  tends  to  become  heated  the  heat  de- 
veloped will  soften  the  grease  and  allow  it  to  run  to  the  spot 
where  it  is  needed.  (2)  Compression  cups  are  used  containing 
a  piston  or  plunger  on  top  of  the  grease  and  acted  on  by  a 
spring  under  control  by  a  screw  operated  by  hand.  (See  Fig. 
176.)  The  grease  is  thus  forced  either  automatically  or  by  hand 
through  the  feeding  tube  and  to  the  bearing.  The  spring  ar- 
rangement may  be  made  adjustable  so  as  to  force  the  grease 
more  or  less  rapidly,  according  to  its  degree  of  hardness,  and  to 
the  rate  of  feed  desired. 

(9)  Lubricator.     For  the  introduction  of  cylinder  oil  into  the 
valve  chests  or  steam  pipes,  an  apparatus  known  as  a  sight-feed 
lubricator  is  very  commonly  employed.     Such  devices  have  been 
made  in  great  variety  of  form,  but  the  description  of  one  will  be 


234  PRACTICAL  MARINE  ENGINEERING. 

sufficient  to  show  the  principle  upon  which  they  operate.  The 
lubricator,  shown  in  Fig.  177,  consists  of  a  main  chamber,  A, 
with  connections  for  attachment  to  the  steam  pipe  or  throttle 
valve  casing  at  B,  and  for  the  attachment  of  a  length  of  vertical 
pipe,  P,  leading  in  to  the  main  steam  pipe  at  C.  D  and  E  are 
two  fittings  for  a  short  length  of  glass  tube,  as  shown.  From 
the  top  of  the  chamber  a  passage  or  pipe  leads  down  to  the  lower 
fitting,  E,  while  from  D  the  passage  leads  into  the  steam  pipe 


Marine  Engineering 

Fig.  176.     Compression  Grease  Cup. 


Fig.  177.     Automatic  Lubricator. 


through  the  connection  at  B.  The  lower  part  of  the  chamber  is 
connected  to  the  vertical  pipe  leading  up  to  C.  There  are  also 
two  connections,  F,  G,  with  glass  gauge  between  to  show  the 
level  of  the  oil  and  water  within  the  chamber.  The  operation 
of  the  lubricator  depends  on  the  difference  in  density  between 
the  oil  and  water.  The  lubricator  is  first  filled  with  oil  through 
the  plug  H.  The  steam  is  then  admitted  to  the  pipe,  P,  where 
it  will  slowly  condense  and  collect  at  the  base  of  the  chamber, 
in  the  pipe  between  D  and  E,  and  in  the  pipe  P,  thus  furnishing 
a  head  of  water  acting  on  the  oil  and  forcing  it  upward.  As 


MARINE  ENGINES.  235 

soon  as  the  head  is  sufficient,  oil  will  be  forced  a  drop  at  a  time 
as  regulated  by  the  valve  V,  out  through  the  passage  leading 
from  the  top  of  the  chamber  down  to  E  and  up  through  the 
water  in  the  tube,  DE,  and  so  on  to  the  steam  pipe,  where  it  is 
caught  by  the  flow  of  steam  and  carried  to  the  valve  chest  and 
cylinder.  The  passage  of  the  oil  drop  upward  is  plainly  seen, 
and  thus  the  operation  of  the  lubricator  is  under  ready  observa- 
tion. Such  lubricator  may  be  placed  on  the  steam  pipe  or  throt- 
tle valve  chamber,  or  at  any  convenient  point  where  the  oil  will 
be  carried  by  the  inflowing  steam  to  the  points  where  needed. 

(10)  Oil  Pump.  A  simple  arrangement  for  forcing  cylinder 
oil  into  a  steam  chest  is  sometimes  used  when  it  is  not  conven- 
ient to  fit  a  lubricator.  This  consists,  as  shown  in  Fig.  178,  of 


Marine 

Fig.   179.     Oil   Pump. 

an  oil  pump  operated  by  hand.  The  chamber  being  filled  with 
oil  the  delivery  valve  is  opened  and  the  oil  forced  in  as  may  be 
desired,  through  a  connection  attached  to  the  pump  delivery,  as 
shown. 

(n)  Modern  Systems  of  Oil  Distribution.  In  the  preceding 
section  we  have  described  the  principal  devices  used  for  supply- 
ing oil  to  a  bearing,  or  to  a  steam  pipe  or  chest.  We  will  now 
describe  briefly  the  general  oiling  system  for  the  engine  as  a 
whole,  involving  such  combination  of  these  devices  as  may  be 
found  most  desirable. 

The  leading  features  of  the  modern  system  consists  in  the 
provision  of  a  small  number  of  distributing  centers  from  which 
oil  is  taken  by  piping  as  directly  as  possible  to  the  various  places 


236  PRACTICAL  MARINE  ENGINEERING. 

where  needed,  each  place  having  its  own  independent  pipe  and 
set  of  connections.  Following  is  a  brief  description  of  such  a 
system  of  oiling  gear,  and  will  serve  to  illustrate  the  methods 
now  in  use  in  good  practice. 

A  light  cast  brass  box  is  provided  for  each  cylinder  placed 
at  a  point  higher  than  any  joint  or  bearing  to  be  reached  by  the 
oil,  and  having  a  capacity  sufficient  to  last  several  hours  without 
refilling.  These  oil  boxes  are  provided  with  sight  feed  cups  with 
protected  glass  tubes  from  which  pipes  lead  to  wipers  on  the 
moving  parts,  or  to  tubes  in  the  bearings  and  guides.  Union 
joints  are  fitted  where  necessary,  so  that  the  oil  pipes  may  be 
quickly  taken  down  and  cleaned.  With  few  exceptions  the  oil 
for  the  various  moving  parts  of  the  cylinder  is  supplied  from 
this  box. 

The  main  crank  pin  is  oiled  by  means  of  a  pipe  and  cup 
carried  on  the  cross-head  and  taking  oil  from  a  drip  supplied 
from  the  oil  box  as  described.  The  pipe  runs  down  the  side  of 
the  rod,  or  frequently  inside  if  the  rod  is  hollow,  and  connects 
with  the  oil  duct  leading  through  to  the  pin.  The  cross-head 
guides  are  provided  with  oil  through  pipes  connected  with  holes 
at  about  the  middle  of  each  forward  and  backing  guide.  The 
main  pillow-blocks  are  oiled  by  one  or  more  wick  cups  deliver- 
ing the  oil  at  the  points  desired. 

A  cup  for  tallow  or  grease  is  also  usually  provided,  and  like- 
wise sometimes  a  hole  through  which  the  hand  may  be  passed 
to  feel  of  the  shaft  as  may  be  desired.  The  presence  of  this 
hole,  however,  is  not  in  accord  with  the  principles  given  above 
in  (i),  and  the  practice  cannot  be  recommended.  If  anything  of 
the  kind  is  to  be  fitted  it  is  better  to  carry  the  hole  simply 
through  the  cap,  thus  leaving  the  brass  continuous.  The  latter 
may  then  be  felt  as  desired,  and  a  tendency  to  heat  may  be  thus 
observed.  The  excentric  straps  are  fed  from  long  narrow  oil 
cups,  receiving  their  oil  through  the  drip  pipes  from  the  reser- 
voir. The  length  of  the  cup  is  made  such  that  some  part  of  it 
is  always  under  the  drip  in  any  position  of  the  excentric.  and  it 
will,  therefore,  always  receive  its  supply.  The  various  other 
parts  of  the  gear  are  similarly  supplied  with  oil  either  from  a 
drip  or  a  wiper  as  may  be  more  convenient. 

The  chief  advantages  of  such  a  system  consist  in  the  cer- 
tainty and  regularity  of  operation  which  may  be  assured  with  the 
minimum  of  time  and  attention  on  the  part  of  the  oiler. 


MARINE  ENGINES.  237 

Sec.  25.  PIPING. 
[i]  Systems  and  Materials. 

The  principal  systems  of  piping  are  as  follows : 

(1)  The  main  steam  piping  from  boilers  to  engine. 

(2)  The  auxiliary  steam  piping  from  the  auxiliary  boiler 
or  from  one  or  more  boilers  specially  selected,  to  the  various 
auxiliaries  which  are  to  be  operated  by  steam. 

(3)  The  main  exhaust  piping  from  cylinder  to  cylinder  and 
from  the  L.  P.  cylinder  to  the  condenser. 

(4)  The  auxiliary  exhaust  system,  providing  each  auxil- 
iary with  its  exhaust,  either  to  the  condenser  or  overboard,  as 
desired. 

(5)  The  feed  system,  main  and  auxiliary  for  returning  the 
condensed  steam  to  the  boilers. 

(6)  The  condensing  system  for  bringing  the  condensing 
water  to  the  condenser  and  for  carrying  it  from  the  condenser 
to  the  sea  again. 

(7)  The  drainage  and  bilge  pump  delivery  systems  for  lead- 
ing water  to  the  bilge  pumps  and  from  the  pumps  to  the  sea. 

(8)  The  fire  system  for  leading  water  to  the  fire  pumps  and 
from  the  pumps  to  the  fire  plugs. 

(9)  The  sanitary  system  for  delivering  water  to  the  W.Cs. 
and  heads. 

(10)  The  steam  heating  system. 

We  may  otherwise  classify  all  pipes  under  three  heads : 
steam  pipes,  exhaust  pipes,  and  water  pipes,  while  of  the  latter  we 
have  a  further  division  into  those  carrying  water  to  a  pump  or 
induction  pipes,  and  those  carrying  water  from  a  pump  or  educ- 
tion pipes. 

For  steam  pipes  the  materials  in  present  use  are  copper, 
wrought-iron,  and  steel.  Copper  pipes  in  small  or  moderate 
sizes  may  be  made  of  seamless  or  solid  drawn  tubing ;  in  large 
sizes  they  are  made  of  sheet  copper  with  brazed  joints. 
Wrought  iron  pipes  are  lap  welded,  while  steel  pipes  are  also  lap 
welded  and  are  sometimes  further  fitted  with  a  riveted  longi- 
tudinal strap  covering  the  line  of  the  weld.  Seamless  or  solid 
drawn  steel  pipes  have  also  been  made  to  some  extent. 

For  the  various  junctions,  elbows,  bends,  tees,  etc.,  steel 
or  malleable  iron  castings  are  used  with  steel  pipe,  while  with 
copper  pipe  sheet  copper  is  used  for  these  parts,  bent  and  formed 


238  PRACTICAL  MARINE  ENGINEERING. 

up   by  hammering  into   shape,   and   secured   at   the   joints   by 
brazing1. 

The  advantages  of  copper  are  its  great  ductility,  freedom 
from  corrosion,  and  the  readiness  with  which  it  may  be  used  to 
make  pieces  of  an  irregular  form,  such  as  the  elbows,  junctions, 
etc.,  referred  to  above.  Its  disadvantages  are,  greater  cost,  low 
tensile  strength,  the  possibility  of  damage  to  the  quality  of  the 
material  in  the  process  of  pipe  manufacture,  and  the  possibility 
of  a  loss  of  ductility  in  service  by  repeated  strains  due  to  the 
expansions  and  contractions  which  result  from  changes  in  tem- 
perature. 

The  metal  close  about  a  flanged  joint  seems  especially 
liable  to  lose  its  strength  in  this  way.  This  is  probably  due  to 
the  concentration  of  the  strains  due  to  expansions  and  con- 
tractions in  the  vicinity  of  a  rigid  connection  such  as  a  flanged 
joint,  and  to  the  development  in  this  way  of  a  line  of  weakness 
running  around  the  pipe. 

To  render  copper  pipe  more  secure  under  high  pressure  it 
has  been  wound  with  copper  or  steel  wire,  or  reinforced  by 
wrought-iron  or  steel  bands.  Such  bands  may  be  from  ^  to  2 
inches  wide  by  y&  to  J4  inch  thick,  and  spaced  with  intervals  of 
from  6  to  10  inches.  These  methods,  especially  the  latter,  have 
proven  quite  successful  in  strengthening  copper  piping  for  mod- 
ern advancing  pressures. 

The  chief  advantage  of  wrought  iron  and  steel  pipes  are, 
less  cost,  greater  tensile  strength,  less  liability  of  the  mater- 
ial to  damage  in  quality  in  the  processes  of  manufacture,  and 
less  liability  to  lose  strength  or  ductility  in  service.  Their 
disadvantages .  are,  greater  liability  to  corrosion,  and  greater 
weight  of  cast  junctions  and  fittings  than  for  copper. 

Welded  pipe  is  made  from  rolled  strips  the  edges  of  which 
are  machine  beveled  for  a  lap  joint.  The  requirements  of  manu- 
facture are  such  that  for  all  except  the  largest  sizes  the 
thickness  is  in  excess  of  that  needed  for  strength  alone,  at  least 
with  the  pressures  at  present  in  use,  so  that  when  such  material 
is  employed  there  is  always  an  excess  of  strength.1 

With  wrought-iron  pipes  the  welded  joint  is  trusted  without 
reinforcement.  With  mild  steel  a  covering  strip  or  butt  strap 
is  sometimes  riveted  on,  though  with  the  later  improvements  in 
the  welding  quality  of  such  material,  experience  shows  that  these 
joints  are  quite  as  reliable  as  those  of  iron.  Flanges  for 


MARINE  ENGINES. 


239 


wrought-iron  or  steel  pipes  may  be  welded  on,  but  more  com- 
monly they  are  riveted  or  screwed  to  the  pipes.  In  the  latter 
cases  the  flanges  are  caulked  on  both  sides  to  make  a  steam 
tight  joint. 

In  small  sizes  and  in  a  relatively  cheaper  grade  of  practice, 
ordinary  commercial  steam  piping  is  used,  fitted  up  with  the 
usual  fittings  and  screwed  joints. 

For  exhaust  piping  the  same  general  character  of  pipe  is 
used  as  for  steam,  with  such  differences  as  the  decreased  strength 
necessary  may  indicate. 

For  water  piping  steel,  iron  and  copper,  and  in  cheaper 
practice  the  ordinary  commercial  pipe  are  all  used.  Steel  and 
iron  are  usually  considered  less  suitable  for  water  than  for 
steam  piping  on  account  of  the  greater  danger  from  corrosion. 
This  is  especially  true  for  feed  piping,  and  in  case  such  material 
is  used  for  this  purpose  it  is  considered  good  practice  to  care- 
fully galvanize  the  pipe  both  inside  and  out.  It  is  likewise  good 
practice  to  tin  all  copper  piping  which  is  under  the  floor  plates 
or  in  the  bilge,  but  this  is  rather  to  protect  the  ship  than  the 
pipe,  the  former  being  in  danger  of  attack  by  electro  chemical 
action  (see  Sec.  40)  in  case  the  copper  and  the  metal  of  the 
ship  obtain  connection  through  a  medium  such  as  bilge  water. 
In  connection  with  piping  see  also  that  heading  under  Section  19. 

[2]  Expansion  Joint. 

The  expansion  and  contraction  of  a  length  of  piping  under 
a  change  of  temperature  require  some  kind  of  joint  or  connec- 


Fig.  179.     Expansion    Joint. 

tion  which  will  allow  of  the  change  of  length  without  buckling  or 
straining  the  pipe.  This  is  usually  provided  by  an  expansion  joint, 
as  shown  in  Fig.  179.  This  consists  of  a  recessed  portion  on 
one  part  of  the  joint  into  which  the  other  fits,  as  shown.  The 


240  PRACTICAL  MARINE  ENGINEERING. 

space  left  between  the  two  thus  forms  a  stuffing-box  into  which 
packing  is  compressed  by  means  of  the  gland.  The  two  parts 
of  the  joint  are  thus  free  to  slip  a  little  way,  one  relative  to  the 
other,  while  the  joint  is  kept  tight  by  means  of  the  stuffing  box 
and  gland  in  the  usual  manner.  It  is  readily  seen  that  the  steam 
pressure  within  the  pipe,  especially  if  it  contains  a  bend  or  el- 
bow, will  tend  to  force  the  two  portions  of  the  joint  apart,  and 
thus  open  the  pipe  at  the  joint.  To  guard  against  this,  safety 
stays  or  ties  should  be  fitted.  In  the  figure  one  of  three  such 
stays  is  shown  by  the  bolt  at  the  top.  Care  must  be  taken  in 
adjusting  such  stays  that  sufficient  freedom  is  left  for  the  expan- 
sion and  contraction  which  the  joint  is  intended  to  provide  for. 

In  special  and  more  complicated  forms,  known  as  balanced 
or  equilibrium  expansion  joints,  these  forces  are  more  or  less 
completely  balanced  within  the  joint  itself. 

[3]  Globe  Angle  and  Straightway  Valves. 
For  controlling  the  flow  of  a  liquid,  vapor  or  gas  through  a 
line  of  piping,  various  forms  of  valve  are  used.  Chief  among 
these  are  the  Globe,  Angle  and  Straightway  or  Gate  types,  as  de- 
scribed in  Section  24  [i],  [2],  and  to  which  reference  may  be 
made. 


AUXILIARIES. 


241 


CHAPTER  V. 

AUXILIARIES. 

Sec.  26.  CIRCULATING  PUMPS. 

The  office  of  the  circulating  pump  is  to  draw  the  condensing 
water  from  overboard,  force  it  through  the  condenser  tubes,  as 
explained  in  Section  29,  and  thence  overboard  through  the  con- 
denser discharge  pipe.  The  principal  resistance  to  be 


n/w  Engineering 


Fig.  180.     Centrifxigal    Pump. 

come  by  the  pump  is  the  resistance  to  the  llo\v  of  the  water 
through  the  tubes,  and  this  is  but  slight  measured  in  pounds  per 
square  inch  or  in  feet  of  head.  On  the  other  hand,  the  quantity 
of  water  to  be  handled  is  large,  and  hence  the  requirement  is 
for  a  type  of  pump  which  shall  be  able  to  handle  large  quantities 
of  water  against  a  small  head  or  resistance.  These  require- 
ments are  very  perfectly  fulfilled  by  the  centrifugal  pump,  as 
shown  in  Fig.  180.  The  moving  part  consists  of  a  number  of 


242 


PRACTICAL  MARINE  ENGINEERING. 


vanes  or  arms  attached  to  a  shaft  and  forming  what  is  called 
the  runner.  This  revolves  within  a  casing  furnished  with  inflow 
and  outflow  passages,  as  shown  in  the  figure.  The  pump  being 
primed  or  filled  with  water  and  started,  the  rotary  motion  gives 
rise  to  a  centrifugal  force,  in  obedience  to  which  the  water  moves 
outward  toward  the  tips  of  the  blades,  where  it  escapes  through 
the  outflow  passage  into  the  discharge  pipe.  There  is  a  corre- 
sponding defect  of  pressure  about  the  hub  of  the  runner  and  a 
resulting  inflow  of  water  from  the  sea  to  take  the  place  of  that 
which  leaves  at  the  outflow.  The  operation  thus  becomes  con- 


Fig.  181.    Outboard  Discharge  Valve. 

tinuous  and  results  in  a  steady  flow  of  water  from  the  pump 
through  the  condenser  tubes  and  back  to  the  sea  through  the 
condenser  discharge  pipe  and  outboard  delivery.  In  order  to 
prevent  the  water  from  "short  circuiting"  or  slipping  back  from 
the  discharge  space  about  the  tips  of  the  blades  to  the  inflow 
space  about  the  hub,  a  running  fit  is  provided  between  cor- 
responding faces  on  the  runner  and  casing  as  indicated  in  the 
figure. 

The  discharge  or  outboard  delivery  valve  is  usually  a  plain 
type  of  angle  stop  valve,  as  illustrated  in  Fig.  181.    Its  office  is 


AUXILIARIES.  243 

simply  to  allow  when  open  the  discharge  of  the  water  from  the 
condenser,  and  prevent  when  closed  the  inflow  of  the  sea  to  the 
pump. 

Sec.  27.  CONDENSERS. 

The  purpose  of  the  condenser  is  to  provide  for  converting 
the  exhaust  steam  back  into  water.  Condensers  are  of  two 
types — jet  and  surface. 

The  jet  condenser  consists  simply  of  a  chamber  of  rec- 
tangular or  cylindrical  form  in  which  the  steam  and  the  conden- 
sing water  are  mingled  together,  the  steam  giving  up  its  heat  to 
the  relatively  cool  water,  and  thus  being  reduced  to  the  liquid 
state  again.  The  water  is  usually  led  into  the  top  of  the 
chamber  and  allowed  to  fall  upon  a  plate  pierced  with  a  large 
number  of  small  holes,  and  known  as  the  scattering  plate.  This 
divides  the  water  into  small  streams  or  jets  and  enables  it  to  mix 
intimately  with  the  steam  which  enters  just  below  the  plate.  The 
condensed  steam  and  condensing  water  then  fall  together  to  the 
bottom  of  the  condenser.  From  here  the  water  is  removed 
by  the  air-pump  which  delivers  it  overboard,  the  feed-pump  in 
the  meantime  taking  enough  for  the  boiler  feed  and  returning  it 
to  the  boilers. 

The  usual  type  of  surface  condenser  consists  of  a  chamber 
commonly  of  cylindrical  form  if  separate  from  the  main  engine 
(see  Fig.  182),  or  rectangular  if  forming  a  part  of  the  engine 
columns.  (See  Fig.  100.)  This  chamber  contains,  as  shown, 
a  large  number  of  small  brass  tubes  running  between  the  inner 
walls  of  the  heads,  which  are  double,  thus  providing  a  connec- 
tion between  the  ends  of  the  various  tubes.  The  condensing 
water  is  driven  by  the  circulating  pump  through  the  tubes,  the 
usual  run  being,  as  shown  in  the  figure.  The  water  enters  at 
the  lower  left  hand  end  and  fills  the  lower  half  of  the  head,  be- 
ing prevented  from  filling  the  whole  head  by  a  partition  half  way 
up,  as  shown.  It  thus  finds  its  way  into  the  lower  half  of  the 
tubes  and  flows  through  them  to  the  right  hand  head.  It  then 
rises  into  the  upper  half  of  the  tubes,  flows  back  to  the  left  and 
out  at  the  opening  in  the  upper  part  of  the  left  hand  head.  The 
water  thus  traverses  twice  the  length  of  the  condenser  forward 
and  back,  and  from  the  bottom  upward.  The  steam,  on  the  other 
hand,  enters  at  the  top  into  the  body  of  the  chamber,  and  thus 
around  the  outside  of  the  tubes.  The  steam  and  the  condensing 
water  are  thus  kept  separate,  and  the  steam  is  condensed  simply 


244 


PRACTICAL  MARINE  ENGINEERING. 


by  the  surface  action  of  the  tubes.  The  steam  thus  condensed  to 
water  falls  to  the  bottom  of  the  condenser,  whence  with  some  air 
and  vapor  it  is  removed  by  the  air-pump  and  delivered  to  the  hot- 
well,  whence  it  is  taken  by  the  feed-pump  and  sent  back  to  the 
boilers.  Baffle  or  diaphragm  plates,  as  shown,  are  often  fitted  in 
the  condenser  to  prevent  the  steam  from  rushing  directly 
through  from  the  inflow  on  top  to  the  air  pump  passage  on  the 
bottom.  The  steam  is  thus  forced  to  fill  the  condenser  as  com- 
pletely as  possible,  and  thus  the  condensing  surface  is  more  uni- 
formly brought  into  action.  In  order  to  facilitate  the  rush  of 
steam  downward  into  the  body  of  the  tubes,  thus  bringing  more 


AIR  PUMP  SUCTION 

-    Fig.  182.     Surface    Condenser,    Longitudinal    Section. 

quickly  into  action  those  in  the  lower  part  of  the  condenser,  a 
few  rows  are  often  omitted  in  the  upper  part,  thus  forming 
branching  passages  leading  from  the  top  downward,  as  shown  in 
Fig.  183.  In  order  to  support  the  heads  against  the  pressure 
from  without,  a  certain  number  of  longitudinal  braces  or  struts 
are  necessary,  as  shown  in  the  figures. 

Condenser  shells  are  made  of  cast-brass,  cast-iron,  or  sheet 
brass  or  steel.  When  of  rectangular  form  the  sides  are  cast 
with  the  necessary  webs  to  give  them  strength  to  stand  the  pres- 
sure from  without.  When  of  cylindrical  form  the  necessary 
strength  can  be  given  bv  a  suitable  thickness  of  metal  rein- 


AUXILIARIES,  245 

forced  if  necessary  by  ribs  running  around  the  shell.  When  rela- 
tively thin  sheet  metal  is  employed,  as  in  torpedo-boat  practice 
and  the  like,  it  is  customary  to  fit  one  or  more  angle-iron  or 
Tee-iron  stiffeners  running  around  the  shell  in  order  to  provide 
the  necessary  strength. 

Condenser  tubes  are  of  thin  sheet  brass,  usually  •>£  to  y^ 
inch  outside  diameter.  In  order  to  make  a  water-tight  joint  be- 
tween the  condenser  tubes  and  the  inner  heads  or  tube  plates, 
and  at  the  same  time  to  avoid  a  rigid  constraint  of  the  tube,  a 
great  variety  of  condenser  tube  packings  have  been  employed. 
The  most  common  type  of  packing  in  present  practice  is  shown 
in  Fig-  .184.  The  tube  plate  is  counterbored,  as  shown,  and 
threaded  for  a  ferrule  with  a  tapering  outer  end.  The  hole  in 
the  outer  end  of  the  ferrule  is  thus  of  about  the  same  size  as 


MR  PUMP  SUCTION 

3fartnt  Engineering 


Fig.  183.     Surface  Condenser,   Cross  Section. 

that  inside  the  tube,  and  hence  smaller  than  the  outside  of  the 
tube.  Between  the  other  end  of  the  ferrule  and  the  bottom  of 
the  counterbore  is  usually  a  ring  of  rubber  or  a  few  turns  of  some 
other  elastic  or  fibrous  material  as  packing.  Screwing  clown  on 
the  ferrule  compresses  the  packing,  and  thus  makes  the  joint, 
while  at  the  same  time  the  tube  is  free  to  expand  and  contract 
to  a  slight  extent.  The  outer  ends  of  the  ferrules,  however,  pre- 
vent the  tube  from  crawling  to  such  an  extent  as  to  free  either 
end,  a  result  liable  to  occur  without  some  method  of  prevention. 

Sec.  28.  AIR  PUMPS. 

It  is.  the  purpose  of  the  air-pump  to  remove  from  the  con- 
denser the  water  and  such  small  quantities  of  air  as  may  enter 
by  leakage  or  with  the  steam,  and  which  would  ultimately  de- 


246 


PRACTICAL  MARINE  ENGINEERING. 


stroy  the  vacuum  if  riot  removed.  As  often  stated,  it  is  the 
office  of  the  air  pump  to  maintain  the  vacuum  formed  by  the 
condensation  of  the  steam. 

The  usual  type  of  air-pump  is  shown  in  Fig.  185.  A  is  the 
piston  or  bucket  moving  in  the  barrel  B,  and  carrying  bucket 
valves,  D,  opening  upward,  as  shown.  The  foot  valves  at  C  also 
open  upward  and  admit  the  contents  of  the  condenser  from 
below.  Beginning  with  the  piston  in  the  position  shown  the 
operation  is  as  follows : 

As  the  piston  rises,  the  air  and  vapor  between  its  lower 
face  and  the  foot  valves  become  rarified  with  a  resultant  decrease 


Frg.  184.     Ferrule  and  Tube   Packing,   Surface  Condenser. 

of  pressure.  Soon  a  point  is  reached  where  the  pressure  in  the 
condenser  is  decidedly  greater  than  in  the  space  above  the  foot- 
valves,  and  in  answer  to  this  difference  of  pressure  the  valves 
open  and  admit  air,  vapor  and  water  from  the  condenser.  This* 
operation  terminates  with  the  piston  at  the  top  of  the  stroke.  On 
the  return  stroke  the  foot  valves  close  and  the  contents  of  the 
barrel  are  forced  through  the  bucket  valves  at  D  to  the  space 
above.  On  the  next  stroke  the  contents  are  lifted  and  forced 
out  through  the  delivery  or  head  valves  at  E,  wrhere  the  air  and 
vapor  escape,  and  the  water  flows  to  the  hot-well,  whence  it 
is  sent  by  the  feed-pump  back  to  the  boiler. 


AUXILIARIES. 


247 


Fig.  185.    Vertical  Attached  Air  Pump. 


248 


PRACTICAL  MARINE  ENGINEERING. 


It  is  evident  that  the  pressure  in  the  condenser  cannot  be 
reduced  below  that  necessary  to  raise  the  foot-valves,  so  that 
for  this  reason,  as  well  as  for  their  more  ready  response  to  varia- 
tion of  pressure,  they  should  be  made  as  light  as  is  consistent 
with  a  proper  performance  of  their  duty.  As  shown  in  Fig.  186, 
such  valves  in  modern  practice  are  usually  made  of  light  sheet 
metal  discs  controlled  by  spiral  springs.  In  older  practice  vul- 
canized rubber  was  quite  commonly  employed.  It  is  also  evi- 
dent that  the  foot  valveb  will  respond  the  more  quickly,  the  more 
rapidly  the  pressure  above  them  decreases  as  the  piston  begins  to 
rise,  and  hence  the  less  the  clearance  space  between  the  valves 
and  the  piston  when  in  its  lowest  position. 

The  air-pump  has  this  peculiarity  in  its  action,  that  the 
load  per  stroke  and  hence  the  resistance  often  dUreases  with  an 
increase  of  speed,  and  increases  with  a  decrease  of  speed.  Hence 
when  the  pump  is  operated  by  an  independent  engine,  it  may 


Fig.  186.    Air  Pump  Valve,  Guard  and  Spring. 

be  liable,  unless  carefully  designed,  to  race  or  run  away  to  ex- 
cessively high  speeds  with  an  increase  of  pressure  in  the  steam 
cylinder,  or  to  slow  down  and  stop  with  a  corresponding  de- 
crease. 

It  is  apparent  also  that  a  certain  time  will  be  needed  for 
the  foot  valves  to  open,  and  for  the  air,  water  and  vapor  to  flow 
through.  Hence,  with  excessive  speeds,  the  valves  may  not  have 
time  to  open  between  strokes,  the  vacuum  will  become  poorer, 
'and  the  condenser  may  become  flooded  with  water.  It  thus  fol- 
lows that  with  too  high,  as  well  as  with  too  low  a  speed,  the 
vacuum  will  be  poor,  and  the  operation  of  the  pump  unsatis- 
factory. 

The  air-pump  may  be  driven  either  by  an  independent  en- 
gine, or  by  attachment  to  the  main  engine.  The  attached  air- 


AUXILIARIES. 


249 


pump  is  usually  operated  by  air  pump  levers,  which  derive  their 
motion  in  most  cases  from  the  L.  P.  cross-head,  as  shown  in  Fig. 
<*<;.  The  stroke  of  the  pump  is  thus  reduced  to  usually  less 
than  one-half  that  of  the  main  engine.  One  of  the  advantages 
of  the  attached  air-pump  is  that  the  number  of  strokes  per  min- 
ute is  necessarily  the  same  as  for  the  main  engine,  and  it  can 
neither  race  nor  slow  clown  on  account  of  variations  in  its  own 
resistance.  A  further  advantage  is  that  the  power  required  for 
its  operation  is  obtained  more  economically  than  when  operated 
by  a  separate  engine.  The  chief  disadvantage  of  the  attached 
air-pump  is  that  with  the  modern  increase  of  revolutions,  the 
speed  may  be  too  great  "for  the  best  results  from  the  pump  as 


Fig.  187.     Air  Pump  for  High  Speeds. 

usually  designed.  This,  together  with  the  advantage  of  having 
the  condition  of  the  condenser  under  control  independent  of  the 
main  engine  furnish  the  chief  reasons  for  the  use  of  the  inde- 
pendent air-pump.  When  thus  fitted  as  an  independent  auxil- 
iary the  number  of  double  strokes  per  minute  usually  varies 
from  15  or  20  to  30  or  more,  while  the  revolutions  of  the  main 
engine  may  be  from  100  to  200  or  more. 

For  special  cases  where  the  revolutions  are  very  high,  as  in 
torpedo  boat  practice,  but  where  for  simplicity  or  for  the  saving 
of  space  it  is  desirable  to  use  an  attached  air-pump,  the  Bailey 
type  of  pump  is  employed.  In  this  pump,  as  shown  in  Fig.  187, 


250 


PRACTICAL  MARINE  ENGINEERING. 


the  water  flows  by  gravity  into  the  barrel  through  ports  alter- 
nately opened  and  closed  by  the  piston  itself,  which  thus  serves 
as  its  own  valve.  The  air  and  vapor  naturally  expand  and  enter 
with  the  water,  and  the  whole  contents  are  forced  out  of  the 
end  of  the  barrel  through  delivery  valves  similar  to  those  in  the 
pump  of  usual  type.  In  some  cases  the  delivery  valves  are  car- 


Fig.  188.    Vertical   Independent   Air   Pump. 

ried  on  movable  heads,  which  thus  become  valves  in  themselves, 
and  available  to  relieve  the  barrel  in  case  the  smaller  valves  give 
insufficient  opening.  In  some  cases,  as  shown  in  Fig.  187,  the 
smaller  valves  are  omitted  and  the  entire  head  serves  as  the  de- 
livery valve.  With  this  design  air-pumps  may  be  successfully 
operated  at  speeds  of  400  or  500  revolutions  and  higher. 


AUXILIARIES.  251 

When  operated  independently  the  air  pump  is  very  com- 
monly made  double,  and  operated  by  one  form  or  another  of 
special  steam  valve  gear.  A  typical  form  of  independent  air 
pump  is  shown  in  Fig.  188.  The  general  operation  of  the  valve 
gear  is  as  follows  :  The  beam  which  positively  connects  the  main 
piston  rods  of  the  pumps  operates  from  a  point  near  its  center 
and  by  means  of  rod  and  bell  cranks,  the  slide  valve  of  the  hori- 
zontal cylinder  which  lies  between  the  main  steam  cylinders,  as 
shown.  The  piston  of  this  horizontal  cylinder  is  really  the  driv- 
ing engine  of  the  main  steam  valves,  a  function  which  it  per- 
forms by  means  of  a  system  of  internal  levers.  See  further  Sec- 
tion 33  regarding  the  operation  of  such  types  of  pump  valve 
gear.  The  adjustable  collars  on  the  valve  stem  of  the 
"valve  driving  engine"  afford  a  means  for  regulating 
for  full  stroke  at  any  speed,  while  suitable  cushion  valves  give  a 
further  control  over  the  action  during  the  stroke,  in  regulating 
the  distribution  of  the  work  and  preventing  the  slamming  of 
the  foot  valves. 

Sec.  29.  FEED  PUMPS  AND  INJECTORS. 

Comparing  the  feed  and  circulating  pumps  we  find  that 
the  former  has  to  handle  a  very  much  smaller  quantity  of  water — 
usually  from  1-25  to  1-40  the  amount — but  against  a  very  much 
higher  pressure,  viz.,  that  in  the  boilers.  In  consequence  an 
entirely  different  type  of  pump  is  required. 

The  feed-pump  may  be  attached  to  the  main  engine,  or  run 
as  an  independent  auxiliary.  When  attached  to  the  engine  it 
is  usually  of  the  type  known  as  the  plunger  pump  and  shown  in 
Fig.  189.  The  moving  part  consists  simply  of  the  plunger,  AB, 
working  in  the  stuffing  box,  KL,  and  operated  usually  from  the 
air-pump  levers.  There  are  two  valves  or  sets  of  valves,  in- 
flow and  outflow,  as  shown  at  F  and  E.  The  level  of  the  pump 
is  usually  below  that  of  the  hot-well  so  that  the  water  stands 
ready  to  enter  through  the  inflow  valves  as  the  plunger  rises  and 
makes  room  for  it.  This  is  aided  by  the  partial  vacuum  formed 
within  the  barrel  as  the  plunger  rises.  On  the  other  hand,  as  the 
plunger  descends  on  the  next  stroke  the  inflow  valve  closes  and 
the  water  flows  out  through  the  outflow  valve  in  order  to  make 
room  for  the  descending  plunger.  It  is  thus  seen  that  the  pump 
is  single  acting ;  that  is,  that  it  delivers  but  once  in  two  strokes, 
and  that  the  amount  delivered  is  measured  by  the  volume  of  the 
plunger  displacement. 


252 


PRACTICAL  MARINE  ENGINEERING. 


This  in  turn  equals  the  cross-sectional  area  of  the  plunger 
multiplied  by  the  length  of  the  stroke.  The  actual  delivery  per 
stroke  will  be  somewhat  less  than  this  due  to  leakage,  and  to 
failure  of  the  barrel  to  completely  fill  on  the  up  stroke. 

The  stuffing  box,  K  L,  is  of  course  accessible  and  adjustable 
from  the  outside,  and  with  proper  design  the  inflow  and  outflow 
valves  may  be  examined  by  the  simple  removal  of  a  bonnet. 
The  strong  points  of  this  pump  are  its  simplicity,  and  the  ready 
accessibility  for  examination  and  adjustment,  of  all  parts  on 
which  the  operation  of  the  pump  may  depend. 


Fig.  189.     Plunger    Feed    Tump. 

In  fitting  up  the  attached  feed  pump  it  is  necessary  to  pro- 
vide  it  with  some  form  of  safety  or  relief  valve,  else  should  the 
discharge  or  check  valve  jam  or  fail  to  operate,  the  feed  pipe 
or  pump  or  some  part  of  its  operating  gear  would  become 
broken.  Such  a  relief  valve  is  usually  a  simple  form  of  spring 
loaded  safety  valve,  and  similar  to  the  engine  relief  valves  re- 
ferred to  in  Section  24.  In  order  that  the  valve  may  be  ef- 
fective in  relieving  the  pump  and  entire  line  of  pipe  it  should  be 
placed  on  the  pump  chamber  or  in  any  event  not  beyond  the 
pump  discharge  valve. 


AUXILIARIES.  253 

Where  the  feed  pump  is  operated  as  an  independent  auxil- 
iary it  is  usually  of  the  direct  acting  or  positive  motion  type,  as 
described  in  Section  33,  and  to  which  reference  for  details  may 
be  made.  For  feed-pump  purposes  the  area  of  the  steam  piston 
is  made  from  2  to  3  times  the  area  of  the  water  piston  or  plunger 
in  order  to  give  on  the  steam  side  a  pronounced  excess  of  total 
pressure  over  the  resistance  on  the  water  side.  This  will  enable 
the  pump  to  overcome  the  resistance  to  the  flow  of  the  water 
through  the  feed-pipe  and  check  valves,  and  thus  to  force  water 
into  the  same  boiler  from  which  it  draws  its  steam,  or  even  into 
a  boiler  with  a  pressure  somewhat  higher  than  that  from  which 
its  steam  is  drawn.  For  the  general  purposes  of  a  feed  pump 
the  vertical  or  admiralty  style,  as  illustrated  in  Section  33,  has 
come  to  be  very  generally  used.  Its  chief  advantages  over  the 
horizontal  type  are  two  in  number. 

(1)  It  occupies  less  floor  space  and  may  be  conveniently 
put  up  on  a  bulkhead  or  elsewhere,  in  such  manner  as  to  occupy 
but  little  space  otherwise  available. 

(2)  The  valves  in  the  water  end,  as  shown  in  the  figure, 
are  more  conveniently  arranged  for  examination  by  the  removal 
of  a  bonnet  than  with  the  horizontal  type  of  pump. 

These  considerations  and  especially  the  latter,  have  made 
this  general  type  of  feed  pump  the  standard  in  modern  marine 
engineering  practice. 

In  addition  to  feed-pumps  of  the  plunger  and  piston  types, 
an  injector  is  often  fitted  as  an  auxiliary  means  of  feeding  the 
boilers.  There  are  many  different  varieties  of  injector,  but  a 
description  of  one  will  suffice  to  illustrate  the  principles  in- 
volved. Referring  to  the  diagram.  Fig.  HJO.  S.  is  a  nozzle  con- 
nected with  the  upper  pipe,  I>,  leading  steam  from  the  boiler. 
When  steam  is  turned  on  by  means  of  the  handle,  K,  and  at- 
tached valve-stem  and  valve,  it  escapes  in  a  jet  which  enters  the. 
slightly  tapered  passage  VC.  The  air  in  the  space  around  and 
between  these  two  orifices  is  caught  and  drawn  along  with  the 
jet,  thus  causing  a  reduction  of  pressure  at  this  point.  This 
space  is  connected  through  the  lower  pipe,  B,  to  the  water  reser- 
voir, and  when  the  loss  of  pressure  is  sufficient,  the  water  rises 
the  same  as  in  the  case  of  a  pump.  The  water  and  steam  are 
thus  brought  into  contact,  and  pass  on  together  into  the  com- 
bining and  delivery  tube  CD.  The  steam  is  here  condensed  and 
the  resultant  jet  of  water  attains  a  very  high  velocity.  A  little 


254  PRACTICAL  MARINE  ENGINEERING. 

further  on,  when  this  is  reduced  to  the  relatively  low  velocity  of 
the  water  in  the  feed  pipe,  the  pressure  developed  is  sufficient  to 
overcome  the  boiler  pressure,  to  open  the  check  valve,  and  to 
force  the  water  into  the  boiler. 

It  may  aid  the  understanding  of  this  seemingly  puzzling  re- 
sult if  we  remember  that  it  is  the  energy  of  the  steam  which  is 
the  real  motive  power.  This  is  transformed  largely  into  motion 
in  the  combined  jet,  and  this,  when  arrested,  gives  the  pressure, 
as  stated  before.  In  the  steam  pump  a  steam  piston  is  provided 
much  larger  than  the  water  plunger  in  order  to  give  a  force  suffi- 
cient to  overcome  the  resistance  of  the  feed  pipe  and  at  the 
check  valve.  So  in  the  injector,  in  a  somewhat  similar  manner, 


Fig.  190.     Injector. 

the  energy  of  the  steam  in  a  relatively  large  pipe  is  concen- 
trated on  a  small  jet  of  water,  giving  it  the  high  velocity  and  later 
the  pressure,  as  described. 

In  passing  it  may  be  noted  that  as  a  boiler  feeder  a  good 
injector  has  practically  a  perfect  efficiency,  all  heat  used  being 
carried  back  again  into  the  boiler,  except  the  small  amount  lost 
by  radiation  from  the  instrument  and  connecting  pipes. 

An  injector  of  the  type  shown  in  the  figure  is  known  as  an 
automatic  injector.  This  signifies  that  once  .the  injector  is  ad- 
justed and  working,  should  the  jet  of  water  become  broken  by  a 
jar  or  other  accidental  circumstances,  it  will  restart  itself  without 
further  adjustment.  The  capacity  and  working  range  of  an  in- 


AUXILIARIES.  255 

jector  are  decreased  as  the  lift  is  higher  and  as  the  water  is 
warmer.  With  cold  water  and  a  moderate  lift,  say  not  exceed- 
ing 5  to  8  feet,  a  good  automatic  injector  will  start  up  with  25  or 
30  Ib.  steam  pressure,  and  will  work  with  little  or  no  further 
adjustment  over  a  range  of  perhaps  100  pounds  pressure.  With 
feed  water  at  about  100  deg.  F,  the  same  injector  would  start  at 
30  or  35  Ib.  steam  pressure,  and  will  work  over  a  range  of  per- 
haps about  70  Ib.  or  up  to  about  100  Ib. 

In  addition  to  the  automatic  injector  there  is  another  type 
having  two  sets  of  tubes,  one  for  lifting  and  one  for  forcing. 
Such  instruments  are  often  termined  inspirators  to  distinguish 
them  from  the  ordinary  automatic  injector.  When  properly  ad- 
justed the  lifting  set  of  tubes  acts  as  a  governor  to  the  forcing 
set,  supplying  under  a  great  range  of  steam  pressure  the  proper 
amount  of  water  to  condense  the  steam  in  the  final  set  of  tubes. 
Such  an  injector  handling  cold  water  with  a  short  lift,  will  work 
through  a  range  of  over  200  Ib.,  while  with  water  as  hot  as  100 
deg.  F  and  small  lift  it  will  work  through  a  range  of  from  150 
to  200  Ib.  The  operation  of  each  set  of  tubes  is  on  the  same 
general  principles  as  above  described  for  the  automatic  injector. 

Sec.  30.  FEED  HEATERS. 

The  office  of  the  feed  heater  is  to  raise  the  temperature  of 
the  feed-water  from  that  of  the  hot-well  as  nearly  to  that  within 
the  boiler  as  may  be  practicable  before  the  feed  enters  the  boiler 
proper.  Feed  heaters  are  of  two  fundamentally  different  types, 
according  as  the  heat  used  is  drawn  from  waste  furnace  gases 
or  from  steam.  If  the  former,  as  is  very  common  with  water- 
tube  boilers,  as  described  in  Section  14,  the  feed  heater  is  really 
a  part  of  the  boiler.  The  entire  operation  is  thus  performed  in 
two  stages,  one  in  the  heater,  and  one  in  the  boiler  proper.  In 
the  first  stage  it  is  sought  to  raise  the  water  as  nearly  as  possible 
to  the  boiling  point  by  use  of  the  furnace  gases  after  they  have 
passed  the  main  steam  generating  tubes.  In  the  second  stage, 
carried  out  in  the  boiler  proper,  the  previously  heated  water  is 
transformed  from  liquid  into  vapor. 

The  resulting  economy  comes  from  being  thus  able  to  re- 
duce the  products  of  combustion  to  a  temperature  lower  than 
they  would  otherwise  have  before  finally  getting  rid  of  them. 
The  addition  of  the  heater  will,  of  course,  affect  the  draft,  and 
the  extent  to  which  heating  surface,  either  in  the  form  of  steam 


256  PRACTICAL  MARINE  ENGINEERING. 

generating  tubes  or  feed  heating'  tubes,  can  be  added  without 
seriously  interfering  with  the  draft  is  a  point  which  must  receive 
consideration.  Morever,  since  the  feed-heating  surface  might  be 
put  into  additional  main  boiler  tubes,  thus  giving  the  same  total 
surface  without  a  feed-heater,  the  question  may  naturally  be 
asked  whether  in  such  case  the  results  would  be  as  good.  In 
other  words,  is  it  better  to  put  the  total  heating  surface  all  into 
main  boiler  tube  surface,  or  to  divide  it  up  and  put  a  part 
(usually  quite  small)  into  a  feed-heater  located  beyond  the  mail? 
part  of  the  boiler?  Experience  seems  to  indicate  the  latter  as 
the  better  design  of  the  two,  and  the  fundamental  reason  is  that 
given  above — viz.,  that  we  are  thus  able  to  reduce  the  products 
of  combustion  to  a  lower  final  temperature  than  with  main  boiler 
tubes  of  the  same  aggregate  surface.  The  reason  for  this  is 
found  in  the  fact  that  the  temperature  of  the  feed  water  as  it  en- 
ters the  heater  is  much  lower  than  that  of  the  steam  and  water 
within  the  main  tubes.  Hence  with  such  a  heater  the  gases  as 
they  leave  the  boiler  pass  over  relatively  cool  surfaces,  and  the 
flow  of  heat  will  be  much  more  pronounced,  and  the  gases  will  be 
more  effectively  cooled  than  by  passing  over  an  equal  area  of 
main  boiler  tube  surface. 

Turning  now  to  the  other  type  of  heaters  we  have  an  en- 
tirely different  mode  of  operation.  Here  the  heat  given  the 
feed-water  comes  from  steam  which  is  drawn  either  directly  from 
the  main  or  auxiliary  steam  pipe,  or  from  the  receivers,  or  from 
the  exhaust  of  some  of  the  auxiliaries  on  its  way  to  the  con- 
denser or  to  the  escape  pipe.  There  are  two  styles  of  heater 
working  on  this  principle.  In  one  the  steam  and  feed-water  are 
mixed  together  in  the  same  chamber  and  the  steam  is  condensed 
and  thus  joins  the  feed-water,  raising  its  temperature  as  may  be 
determined  by  the  conditions  of  operation.  In  the  other  style 
the  steam  is  on  one  side  of  a  coil  or  nest  of  tubes  and  the  feed- 
water  on  the  other  side,  the  heat  passing  through  the  metal  of 
the  tubes'from  the  former  to  the  latter  while  the  steam  condensed 
in  consequence  of  the  loss  of  heat  is  drawn  or  trapped  out  as 
may  be  required. 

Where  the  steam  and  feed-water  are  mixed  together  the 
feed-heater  consists  essentially  of  a  chamber  or  drum,  as  in  Fig. 
191,  provided  with  means  for  introducing  the  feed  as  a  spray 
or  series  of  cascades,  while  the  steam  is  introduced  in  jets,  and 
the  two  thus  become  intimately  mingled. 


AUXILIARIES.  257 

In  the  form  here  shown  the  feed  enters  through  C  and  pass- 
ing out  through  a  valve,  D,  falls  as  a  cascade  through  the  an- 
nular space  between  the  pipe  and  the  steam  delivery  drum  which 
is  pierced,  as  shown,  with  small  holes.  The  steam  enters 
through  B,  and  passing  through  the  holes  in  small  jets  becomes 
mingled  with  the  water  and  thus  imparts  to  it  its  heat.  The  t\Vo 
then  fall  to  the  bottom  of  the  chamber  from  whence  the  feed 


TO  CONDENSER 


Fig.  191. 


SUPPLY  TC  SECOND  PUMP 

Feed   Water   Heater,    Direct    Contact. 


pump  takes  its  supply,  and  by  means  of  which  the  water  is  finally 
sent  to  the  boiler. 

The  advantages  of  such  a  form  of  heater  are  simplicity  in  the 
apparatus  itself  and  a  quicker  action  than  with  tubes,  as  in  the 
other  form.  The  chief  disadvantage  lies  in  the  fact  that  an  ad- 
ditional feed  pump  must  be  provided  ;  one  for  forcing  the  water 
from  the  hot-well  to  the  feed-heater  and  the  second  for  taking  it 
from  the  heater  and  forcing  it  into  the  boiler. 


25S 


PRACTICAL  MARINE  ENGINEERING. 


Turning  to  the  other  style  of  heater,  as  illustrated  in  Fig. 
1 92,  we  have  a  chamber  or  drum  containing  a  nest  of  corrugated 
copper  pipe.  The  feed-water  passes  on  one  side  of  the  pipes 
and  the  steam  on  the  other,  as  shown,  the  heat  passing  through 
from  the  one  to  the  other  as  above  described.  Where  such  a 
heater  is  fitted  to  utilize  the  steam  from  an  auxiliary  exhaust,  the 
heater  forms  simply  a  part  of  the  exhaust  passage  and  the  steam 
passes  through  continuously,  simply  leaving  a  part  of  its  heat 
behind. 


RELIEF  VALVE 


SURFACE  BLOW-OFF 


^"AFEED  OUTLET 


EXHAUST 


ELOW-OFF- 

Fig.  192.     Feed  Water  Heater,  Surface. 

In  other  forms  of  heater  there  is  no  continuous  flow  of  steam 
through,  but  the  steam  is  led  to  the  steam  side  from  the  source 
selected  and  there  gradually  condensed  by  the  loss  of  heat,  while 
the  water  thus  formed  is  drawn  off  as  may  be  necessary.  The 
heater  is  thus  kept  cleai  for  efficient  operation,  and  the  water  is 
returned  to  the  hot-well  or  otherwise  into  the  feed  system. 

In  heaters  of  this  type  the  flow  of  water  is  continuous  from 
the  feed-pump  through  the  heater  to  the  boiler,  and  no  additional 
pump  is  required  as  with  the  other  type  referred  to  above.  The 
difference  is  due  to  the  fact  that  where  the  water  and  steam  are 


AUXILIARIES.  259 

separated,  the  water  side  of  the  heater  can  be  operated  under  the 
full  pressure  in  the  feed-pipe  and  thus  made  part  of  the  feed 
circuit.  Where  the  water  and  steam  are  mixed  the  interior  of 
the  heater  cannot  be  operated  under  any  such  pressure,  and  thus 
two  separate  pumps  are  required. 

In  heaters  using  steam  from  the  steam  pipe  or  from  the  re- 
ceivers, it  is  clear  that  all  such  steam  would  ultimately  go  to  the 
condenser  and  thence  back  to  the  boiler  as  feed-water,  and  hence 
that  no  heat  is  saved  which  would  otherwise  have  been  thrown 
away.  In  such  cases  it  is  not  at  first  sight  clear  where  the  gain 
can  come  in,  for  the  operation  seems  to  be  a  simple  shifting  of 
heat  from  one  part  of  the  cycle  to  another  without  gain  or  loss  in 
total  amount.  As  a  matter  of  fact  the  operation  does  consist  of 
just  such  a  shifting  of  heat,  and  here  is  where  the  gain  in  work 
comes  in.  This  shifting  of  heat  from  one  part  of  the  cycle  or 
routine  of  the  steam  to  another  introduces  a  change  which  brings 
the  cycle  a  little  nearer  that  for  the  highest  efficiency  as  described 
in  59.  While  therefore  there  will  be  no  saving  of  heat  as  such, 
the  engine  may  be  enabled  to  better  use  the  heat  which  is  pro- 
vided and  thus  to  show  a  larger  return  in  useful  work.  These 
points  cannot  be  here  discussed  in  detail,  but  it  seems  at  least 
worth  while  to  note  in  general  terms  the  chief  source  of  the 
economy  experienced  with  such  heaters. 

Especially  will  heaters  of  this  type  affect  the  routine  of  the 
steam  favorably  when  they  are  arranged  on  the  compound  or 
step  by  step  principle.  In  this  arrangement  the  feed  passes 
through  a  first  chamber  and  receives  heat  from  steam  drawn 
from  the  low  pressure  receiver.  It  then  passes  on  to  a  second 
chamber  and  there  receives  heat  from  steam  drawn  from 
the  next  higher  receiver,  and  so  on,  in  the  last  receiving 
a  final  addition  of  heat  from  steam  of  full  boiler  pressure. 
This  type  of  heater,  when  of  sufficient  capacity  to  raise  the  tem- 
perature of  the  feed  nearly  up  to  that  of  the  water  in  the  boiler, 
will  effect  a  marked  economy  in  the  engine,  a  saving  presumably 
due  to  the  change  thus  effected  in  the  routine  through  which 
the  steam  is  carried. 

In  addition  to  the  saving  thus  effected  by  feed  heaters,  many 
engineers  believe  that  they  are  of  use  in  reducing  the  strain  and 
wear  and  tear  on  the  boilers  by  furnishing  a  hot  rather  than  a 
cold  feed,  and  hence  that  they  are  of  distinct  advantage  to  the 
boiler  and  well  as  to  the  engine. 


260 


PRACTICAL  MARINE  ENGINEERING. 


Sec.  31.    FH/TERS. 

Feed  water  filters  are  provided  for  removing  oil  from  the 
feed  water  before  it  enters  the  boiler.  See  further  on  this  point 
Section  41.  Such  filters  are  made  in  various  forms,  the  chief 
features  being  the  kind  of  filtering  material  employed,  and  the 
arrangement  of  the  flow  of  water  through  it.  Animal  charcoal;, 
sand,  gravel,  broken  pumice  stone,  etc.,  form  one  class  of  sub- 
stances, while  fibrous  materials  such  as  sponges,  bagging,  towel- 
ing, etc.,  form  another  case.  Of  the  first  class,  animal  charcoal 
is  the  best,  though  somewhat  expensive.  It  may,  however,  be 


Engineering 


Fig.  193.     Feed  Water  Filter. 

removed  from  time  to  time,  washed  in  lye  water  and  replacedr 
and  thus  made  to  do  duty  for  a  long  period  of  time.  The  various 
fibrous  materials,  such  as  sponges  or  bagging,  soon  become 
clogged  also  with  oil  and  impurities,  and  require  either  replace- 
ment or  washing  and  cleaning.  After  a  few  repetitions  of 
cleaning  in  this  manner,  such  material  must  be  replaced  with 
new. 

Filters  also  differ,  according  to  whether  the  flow  of  water 
through  the  filtering  material  is  forced  by  the  pressure  of  the 
feed  pump,  or  is  due  simply  to  the  flow  under  the  action  of 
gravity.  In  gravity  filters  the  flow  may  be  up  and  down,  two  or 


AUXILIARIES.  261 

three  times  through  the  bed  of  filtering  material,  the  course  be- 
ing determined  by  suitable  partitions  or  passages  within  the  filter 
box.  When  the  action  is  under  pressure  the  filter  forms  a  part 
of  the  feed  pipe  circuit  and  the  water  enters  and  passes  through, 
urged  by  the  action  of  the  feed  pump,  though  at  a  much  lower 
velocity  than  through  the  feed-pipe  itself.  In  such  case,  if  the 
filter  should  become  choked,  excessive  pressure  might  be  de- 
veloped between  the  feed-pump  and  filter  with  the  possibility  of  a 
rupture  of  the  latter.  To  avoid  this  danger  a  by-pass  pipe  and 
safety-valve  may  be  arranged  so  that  the  valve  will  open  under 
an  excess  of  pressure  and  allow  the  water  to  flow  around  the 
filter  to  the  continuation  of  the  feed-pipe  beyond.  The  safety- 
valve  may  also  be  maintained  open  by  appropriate  means  and 
the  filter  shut  off  by  stop-valves,  thus  sending  the  feed  through 
the  by-pass  pipe  and  leaving  the  filter  free  for  examination  and 
repair. 

In  Fig.  193  a  simple  form  of  filter  is  shown  with  by-pass  pipe 
and  valves  for  controlling  the  flow  of  the  feed.  From  the  ex- 
planation above  the  operation  of  the  filter  will  be  readily  under- 
stood. 

Sec.  32.  EVAPORATORS. 

The  office  of  the  evaporator  is  to  supply  fresh  water  to  make 
up  the  loss  in  boiler  feed.  Of  the  steam  which  the  boilers  supply 
not  all  can  find  its  way  back  through  the  feed.  Small  steam 
leaks  may  occur  at  the  various  joints  and  stuffing  boxes,  some  of 
the  auxiliaries  may  not  send  their  steam  to  the  condenser,  the 
whistle  may  be  used  (as  in  foggy  weather),  and  so  in  various 
ways  losses  of  fresh  water  will  occur.  The  proportion  of  such 
loss  varies  widely  with  the  circumstances,  but  will  often  amount 
to  5  per  cent,  and  more.  In  order  to  avoid  making  up  this  loss 
with  salt  water  the  evaporator  is  provided. 

A  modern  representative  evaporator  consists  of  a  series  of 
nests  or  coils  of  pipe  contained  within  a  chamber,  as  shown  in 
Fig.  194.  The  chamber  has  a  salt-water  inlet,  and  steam  from 
the  boiler  or  from  one  of  the  receivers  is  passed  inside  the  tubes. 
The  heat  in  the  steam  passes  through  the  tubes  and  forms  steam 
or  vapor  of  lower  pressure  on  the  salt-water  side.  The  chamber 
is  connected  with  the  condenser  or  with  the  low  pressure  re- 
ceiver, and  the  steam  formed  in  the  evaporator  is  thus  passed 
into  the  main  circuit  and  serves  to  make  up  the  loss  as  specified 
before.  At  the  same  time  the  water  formed  in  the  coils  bv  the 


262 


PRACTICAL  MARINE  ENGINEERING. 


loss  of  heat  is  drawn  or  trapped  out  as  it  accumulates,  and  is  re- 
turned to  the  feed,  so  that  all  steam  formed  on  the  salt-water 
side  is  a  net  gain  for  the  fresh-water  account.  The  coils  on  the 
outer  or  salt-water  side  naturally  become  coated  with  scale,  so 
that  they  must  be  cleaned  from  time  to  time.  To  this  end  they 


CROSS  SECTION  OF  EVAPORATOR  COIL 


Fig.  194.    Evaporater. 

are  usually  made  removable  or  arranged  so  as  to  be  readily 
accessible  through  manhole  openings  in  the  shell.  It  is,  of 
course,  essential  that  the  tubes  be  kept  clean  for  the  most  effi- 
cient working  of  the  evaporator. 

In  the  operation  of  the  evaporator  the  chief  point  requiring 
attention  is  the  proper  proportion  between  the  amount  and  tern- 


AUXILIARIES.  263 

peraturc  of  the  inflowing  steam  and  the  pressure  within  the 
chamber  on  the  salt-water  side.  If  the  pressure  is  low  and  steam 
is  provided  in  excess,  it  may  give  rise  to  a  violent  ebullition  or 
foaming,  which  will  carry  some  of  the  salt  water  along  with  the 
vapor  formed,  and  thus  introduce  salt  into  the  circulating  sys- 
tem. This  condition  must  be  guarded  against  by  a  proper  con- 
trol of  the  amount  of  steam  admitted. 

In  the  way  of  general  maintenance,  the  tightness  of  the  tube 
joints  and  the  condition  of  the  tubes  as  regards  scale  are  the 
chief  points  requiring  attention. 

Sec.  33.     DIRECT  ACTING  PUMPS. 

In  early  marine  practice  the  fly-wheel  pump  was  a  favorite 
type,  and  was  used  for  all  ordinary  purposes  where  an  independ- 
ent pump  was  required,  as  for  boiler  feed,  fire  purposes,  or  for 
general  purposes  on  shipboard.  This  pump  consisted  essen- 
tially of  horizontal  steam  and  water  cylinders  with  the  piston  and 
plunger  on  a  common  rod  and  moving  together.  Attached  to 
the  rod  was  a  cross-head  with  connecting  rod  leading  to  a  crank 
and  shaft  carrying  a  fly  wheel.  The  fly  wheel  served  to  carry 
the  pump  past  the  dead  points,  and  the  shaft  served  to  carry  an 
excentric  which  actuated  a  simple  slide  valve  on  the  steam 
cylinder. 

This  type  of  pump,  however,  has  almost  entirely  disappeared 
from  modern  practice,  its  place  being  taken  by  the  direct  acting 
pump  with  its  greater  compactness  of  form  and  better  adapta- 
tion to  the  conditions  of  service. 

We  will  now  consider  briefly  the  essential  features  of  this 
type  of  pump,  with  a  few  examples  drawn  from  modern  practice. 

As  illustrated  in  Fig.  195,  the  pump  is  horizontal  and  con- 
sists of  two  cylinders,  one  for  steam  and  one  for  water,  carried 
on  a  common  piston  rod.  The  steam  end  is  operated  by  means 
of  a  suitable  valve  gear  as  a  simple  reciprocating  engine,  and 
thus  communicates  the  same  movement  to  the  pump  plunger  or 
piston.  Each  end  of  the  water  cylinder  is  provided  with  both 
inflow  and  outflow  valves,  as  shown,  and  thus  the  pump  becomes 
double  acting, — that  is  delivering  on  each  stroke  alternately  from 
one  end  and  the  other. 

For  operating  the  steam  ends  of  pumps  of  this  type,  a  great 
variety  of  ingenious  valve  gears  have  been  devised. 

The  need  for  special  device  arises  from  the  fact  that  there  is 


264  PRACTICAL  MARINE  ENGINEERING. 

no  rotating  part  and  no  chance  to  use  an  excentric,  and  that  the 
valve  cannot  be  operated  directly  from  the  main  piston  rod. 
Where  it  is  thus  required  that  a  single  set  of  principal  moving 
parts  be  self  operating,  the  valve  gear  usually  consists  of  the 
following  chief  features : 

(i.)  The  main  steam  valve,  often  of  special  form,  but  usu- 
ally operating  as  a  simple  slide  valve. 

(2.)  An  auxiliary  plunger  or  piston  moving  in  a  cylinder 
formed  in  the  valve  chest,  and  coupled  or  connected  to  the  main 
valve. 

(3.)  An  auxiliary  valve  controlling  steam  and  exhaust  to 
and  from  the  two  ends  of  the  auxiliary  plunger  cylinder. 

(4.)  Means  for  operating  the  auxiliary  valve  from  the  main 
piston-rod.  Such  means  may  consist  of  levers,  links,  rods,  cams, 
etc.,  operated  by  tappets  on  the  main  rod,  whose  location  or 
point  of  operation  may  be  adjusted  according  to  the  length  of 
the  stroke  desired. 

The  chain  of  operation  is  then  in  general  as  follows : 

Just  before  the  end  of  the  stroke  the  tappet  or  other  piece 
moved  by  the  main  piston  rod  gives  motion  to  the  auxiliary 
valve.  This  produces  an  adjustment  of  steam  and  exhaust  for 
the  auxiliary  cylinder  which  results  in  a  movement  of  the  auxil- 
iary piston  and  hence  the  movement  of  the  main  valve  as  de- 
sired. The  motion  of  the  main  piston  is  thus  reversed  and  the 
stroke  takes  place  in  fhe  opposite  direction,  and  so  on  continu- 
ously. 

In  Fig.  195  the  lower  section  is  horizontal  and  taken  through 
the  auxiliary  piston  and  auxiliary  slide  valve  operated  by  the 
levers  and  links  as  shown.  The  upper  view  shows  in  vertical 
section  the  auxiliary  piston  and  main  steam  valve. 

If  two  such  pumps  are  placed  side  by  side,  it  is  found  that 
the  valve  of  each  pump  may  be  operated  from  the  piston  rod  of 
the  other.  Hence  by  appropriate  connections  a  pair  of  such 
pumps  may  be  made  self  operative,  the  strokes  being  made  alter- 
nately, and  each  piston  rod  running  the  valve  gear  of  the  other 
pump.  Such  an  arrangement  constitutes  a  dnplc.v  pump,  a  form 
which  has  enjoyed  w^ide  and  continued  favor  among  marine  en- 
gineers for  feed-pumps  and  for  other  purposes  with  generally 
similar  conditions. 

In  the  so-called  "Admiralty"  style  of  pump  the  motion  of 
these  parts  is  vertical,  and  the  water  valves  are  specially  arranged 


AUXILIARIES. 


265 


with  a  view  to  ready  examination  and  overhauling.  As  noted  in 
Sec.  29,  this  general  style  is  quite  commonly  used  for  feed-pump 
purposes.  Such  pumps  may  be  either  simple  or  duplex,  but  the 
duplex  type  is  more  commonly  met  with  in  this  form.  In  Fig. 
196  is  shown  one  member  of  a  duplex  admiralty  pump,  the  ar- 
rangement of  the  parts  and  operation  of  which  will  be  apparent 
without  further  explanation.  In  Fig.  197  is  shown  similarly  a 
single  vertical  type  of  feed-pump  with  independent  valve  gear, 


Marint  E.iytnterfng 


Fig  19").     Direct  Acting  Independent  Feed  Pump. 

the  auxiliary  piston  being  operated  by  the  opening  and  closing 
of  ports  due  to  a  rocking  motion  which  is  communicated  to  it  by 
the  levers  and  link  work  as  shown. 

Bilge  pumps  when  independent,  and  all  general  service 
pumps,  are  usually  of  the  direct  acting  form  as  above  illustrated. 
The  chief  item  of  difference  is  found  in  the  ratio  of  the  areas  of 
steam  piston  and  water  plunger.  Where  the  water  is  to  be  de- 


266 


PRACTICAL  MARINE  ENGINEERING. 


livered  under  considerable  pressure,  as  for  feed-pumps  or  for  fire 
purposes,  the  area  of  steam  piston  will  be  from  two  to  three 
times  that  of  water  plunger.  Where  the  resistance  to  be  over- 
come is  less,  as  in  a  pump  for  freeing  the  bilge  or  for  circulating 


Fig.  196.     Vertical  Duplex  Feed  Pump. 
Admiralty  Type. 


Marine  Engineering 

Fig.  197.     Vertical  Single  Feed 


water  through  distillers,  evaporators,  water-closets,  etc.,  the 
water  plunger  may  be  relatively  larger  and  we  shall  find  such 
pumps  with  a  water  end  only  slightly  smaller  or  equal  in  size  or 
even  larger  than  the  steam  end. 


AUXILIARIES.  267 

Such  pumps  are  always  so  connected  up,  of  course,  as  to 
enable  them  to  be  run  from  the  auxiliary  boiler. 

Sec.  34.    BLOWERS  OR  FANS. 

The  centrifugal  blower  is  the  type  universally  used  on  ship- 
board for  all  purposes  requiring  the  handling  of  large  quantities 
of  air  under  light  pressure,  as  for  ventilation  and  forced  draft. 

As  indicated  in  Figs.  95,  96,  such  a  blower  consists  of  a 
series  of  flat  or  nearly  flat  steel  vanes  carried  on  a  shaft  and  sur- 
rounded by  a  casing.  The  principle  of  operation  is  the  same  as 
with  the  centrifugal  pump,  as  described  in  Sec.  26.  The  rotation 
of  the  vanes  sets  up  first  a  circular  current  or  rotation  of  the  air, 
and  as  a  result  of  this  motion,  centrifugal  force  is  developed 
which  carries  the  air  out  toward  the  tips  of  the  blades  and  de- 
velops an  increase  of  pressure  from  the  hub  outward.  If  an  out- 
let is  then  provided  in  the  outer  shell  of  the  casing  the  air  will  be 
delivered  at  this  point  and  the  surrounding  air  will  flow  in  to 
take  its  place  at  the  intake  about  the  hub.  So  long  as  the  rota- 
tion is  kept  up  these  conditions  will  continue,  and  there  will  be  a 
continuous  flow  of  air  in  at  the  hub  and  out  through  the  delivery 
passage  under  a  pressure  depending  on  the  speed  of  rotation  and 
other  circumstances. 

Blowers  are  driven  by  either  steam  engine  or  electric  motor 
direct  connected  to  the  shaft,  and  are  made  of  various  forms  so 
as  to  readily  find  a  place  in  almost  any  position  desired,  thus  re- 
quiring the  smallest  possible  amount  of  otherwise  valuable  space. 

In  the  operation  of  blowers  the  points  of  chief  importance 
relate  to  the  general  care  which  must  be  given  to  the  operating 
motor,  whether  electric  or  steam,  and  to  the  proper  lubrication 
and  care  of  the  fan-shaft  bearings. 

Sec.  35-  SEPARATORS. 

In  many  types  of  water-tube  boilers,  special  arrangements 
are  provided  for  separating  the  steam  from  the  water.  These 
are  usually  located  in  the  upper  drum  or  chamber  and  consist 
commonly  of  one  or  more  metal  plates  pierced  with  holes 
through  which  the  steam  passes  to  the  stop-valve  and  steam 
pipe,  and  which  exercise  more  or  less  of  a  straining  or  separat- 
ing action  on  the  water  and  steam.  Reference  has  been 
made  in  Sec.  16  [4]  to  arrangements  of  this  character. 

In  addition  to  such  arrangements  located  in  the  upper  drum 
of  water-tube  boilers,  special  devices  known  as  separators  are 


268 


PRACTICAL  MARINE  ENGINEERING. 


used  wherever  the  steam  is  likely  to  have  any  considerable  pro- 
portion of  water.  Such  devices  are  found  in  great  variety  of 
form,  and  utilize  various  principles  in  their  operation.  The  most 
successful  are  those  which  employ  for  separating  the  water 
from  the  steam  the  centrifugal  force  developed  by  a  rotation 
of  the  steam  as  it  enters  or  passes  through  the  separating 
chamber. 

The  .following  description  will  serve  to  illustrate  the  oper- 
ation of  a  typical  separator  of  this  character : 

The  separator,  as  shown  in  Fig.  198,  consists  of  a  vertical 
cylinder  with  an  internal  central  pipe  extending  from  the  top 
downward,  for  about  half  the  height  of  the  apparatus,  leaving  an 
annular  space  between  the  two. 


e  Engineering 


Fig.  198.     Separator. 


A  nozzle  for  the  admission  of  the  steam  is  on  one  side,  the 
outlet  being  on  the  opposite  side  or  on  top  as  may  be  most  con- 
venient in  making  the  connections. 

The  lower  part  of  the  apparatus  is  enlarged  to  form  a  re- 
ceiver of  some  considerable  capacity,  thus  providing  for  a  sudden 
influx  of  water  from  the  boiler. 

A  suitable  opening  is  tapped  at  the  bottom  of  the  apparatus 
for  a  drip  connection,  and  a  glass  water  gauge  shows  the  level  of 
the  water  in  the  separator  at  all  times. 

The  current  of  steam  on  entering  is  deflected  by  a  curved 
partition  and  thrown  tangentially  to  the  annular  space  at  the  side 


C  XI  LI  ARIES. 


269 


near  the  top  of  the  apparatus.  It  is  thus  whirled  around  with  the 
velocity  of  influx,  and  a  centrifugal  force  is  developed,  which 
throws  the  particles  of  water  against  the  outer  cylinder.  These 
adhere  to  the  surface,  so  that  the  water  runs  down  continuously 
in  a  thin  sheet  around  the  outer  shell  into  the  receptacle  below, 
while  the  steam,  following  a  spiral  course  to  the  bottom  of  the 
internal  pipe,  enters  it  abruptly,  and  in  a  dry  condition  passes 
upward  and  out  of  the  separator,  without  having  once  crossed 
the  stream  of  separated  water,  all  danger  of  the  steam  taking  up 
the  water  again  after  separation  being  thus  avoided. 

The  water  thus  separated  from  the  steam  collects  in  the 
lower  part  of  the  chamber  and  may  be  drawn  out  from  time  to 
time  or  it  may  be  led  to  a  steam  trap  of  approved  form  and 


Fig.  199.    Ash  Ejector. 

trapped  out,  thus  making  the  operation  entirely  automatic.  The 
water  thus  obtained  will,  of  course,  be  of  high  temperature  and 
should  be  led  directly  to  the  hot-well  where  it  will  aid  in  raising 
the  temperature  of  the  feed-water.  The  heat  which  it  contains 
will  thus  be  returned  to  the  boiler,  and  saved,  and  all  heat  loss 
in  connection  with  the  operation  will  be  avoided. 

Sec.  36.    ASH  EJECTOR. 

Ashes  are  either  hoisted  in  a  bucket  by  a  special  hoist  to  a 
point  on  the  main  deck  level  and  there  dumped  into  an  ash- 
chute  leading  to  the  side  of  the  ship  and  down  into  the  water,  or 
else  disposed  of  directly*  from  the  fire-room  by  means  of  an  ash 
ejector.  Such  a  device  is  illustrated  in  Fig.  199.  A  represents 
a  cast  metal  chute  or  pipe  leading  from  the  fire-room  up  and  out 


270 


PRACTICAL  MARINE  ENGINEERING. 


through  the  side  of  the  ship  near  or  slightly  above  the  water  line. 
At  the  lower  end  this  chute  connects  with  a  hopper,  B,  into 
which  is  led  a  pipe  from  the  discharge  of  a  pump.  This  pipe 
enters  to  a  point  near  the  lower  end  of  the  chute,  into  which  its 
discharge  is  directed,  and  is  contracted  to  a  nozzle  so  that  the 
water  issues  with  a  high  velocity.  The  hopper  may  be  closed  by 
a  cover,  and  if  in  this  condition  the  discharge  valve  is  opened  and 
the  pump  started,  a  stream  issues  with  high  velocity  from  the 
upper  and  open  end  of  the  chute.  If  then  the  cover  is  removed 


Fig.  200.    Ash  Gun. 

and  ashes  shoveled  into  the  hopper,  they  are  caught  by  the 
stream,  carried  rapidly  up,  and  ejected  free  of  the  ship's  side  in  a 
mingled  jet  of  ashes  and  water. 

It  is  found  by  experience  that  at  the  upper  bend  the  wear 
on  the  metal  of  the  pipe,  due  to  the  scouring  action  of  the  ashes, 
is  very  rapid,  and  it  is  usually  found  necessary  to  make  this 
bend  in  a  separate  piece  of  extra  thick  metal,  and  to  provide 
by  means  of  a  proper  arrangement  of  joints  for  its  replacement 
as  occasion  may  require. 


AUXILIARIES. 


271 


A  similar  device  known  as  the  ash  gun  is  shown  in  Fig.  200. 
Where  possible  the  lead  of  pipe  from  the  hopper  to  the  ship's 
side  is  made  straight  .so  as  to  avoid  all  bends  and  elbows.  The 
principles  of  operation  are  the  same  as  above  explained. 


012    8    4    S    67    8    0  10 


48  Murin*  Engineering 

Figs.  201,  202.     General  Arrangement  Plans. 


Sec.  37.    GENERAI,  ARRANGEMENT  OF  MACHINERY. 

We  shall  not  here  discuss  in  detail  the  various  questions 
which  may  arise  in  connection  with  the  problem  of  the  general 
arrangement  of  marine  machinery.  It  will  be  sufficient  for  our 


272  PRACTICAL  MARINE  ENGINEERING. 

present  purpose  to  note  the  fundamental  principles  which  must 
be  held  in  view : 

(i.)  Each  piece  must  be  located  so  as  to  favor,  as  far  as 
possible,  examination  and  repair. 

(2.)  Each  piece  should  be  located  with  reference  to  handi- 
ness  of  care  and  control  in  routine  operation,  and  in  such  way 
as  to  interfere  to  the  smallest  practicable  extent  with  the  routine 
care,  examination  and  repair  of  other  pieces. 

(3.)  Due  regard  must  be  had  to  economy  of  space  and  such 
combinations  of  the  various  pieces  must  be  sought  as  will  re- 
quire the  minimum  total  space,  while  giving  the  necessary  free- 
dom in  accordance  with  the  principles  noted  above. 

(4.)  The  influence  of  the  location  of  the  various  pieces  on 
the  arrangement  of  the  piping  must  be  carefully  noted  and  due 
weight  must  be  given  to  simplicity,  shortness  and  directness  of 
the  various  lines  of  piping. 

In  Figs.  201,  202  are  shown  illustrations  of  a  general  ar- 
rangement plan  in  which  the  condenser  is  located  in  the  engine 
framing.  The  remaining  features  are  independent,  and  include 
those  most  commonly  met  with  in  the  auxiliary  equipment  of  the 
engine  room. 


OPERATION,  MANAGEMENT  AND  REPAIR.  273 


CHAPTER  VI. 

OPERATION,  MANAGEMENT  AND  REPAIR. 

Sec.  38.    BOII/ER  ROOM  ROUTINE. 

In  the  present  section  it  is  the  purpose  to  give  brief  hints 
and  suggestions  regarding  the  routine  of  operation  and  manage- 
ment in  the  fire-room  in  getting  under  way  and  on  the  voyage, 
first  supposing  that  everything  is  working  smoothly  and  with- 
out trouble,  and  then  to  notice  the  chief  emergencies  which  may 
arise.  We  shall  first  suppose  that  fire-tube  boilers  are  in  use, 
and  later  give  such  supplementary  suggestions  as  may  be  suit- 
able for  water-tube  boilers. 

[i]  Starting  Fires  and  Getting  Under  Way. 

A  general  examination  must  first  be  made  of  the  boiler  and 
fire-room  equipment  in  order  to  make  sure  that  everything  is  in 
readiness  for  getting  up  steam.  Among  the  more  important 
points  to  be  attended  to  the  following  may  be  mentioned : 

See  that  the  coal  bunker  doors  are  in  proper  working  order 
and  if  the  bunker  is  partly  empty  it  may  be  well  to  air  it  by  open- 
ing the  door  and  taking  off  the  deck  plates. 

See  that  the  coal  handling  gear  is  on  hand  and  in  proper 
condition. 

See  that  the  necessary  fire  tools  are  provided,  and  dis- 
tributed as  needed. 

Examine  the  grate-bars,  bridge-walls  and  back-connections, 
and  note  whether  the  area  of  passage  above  the  bridge-walls  is 
properly  proportioned.  For  usual  conditions  it  should  be  from 
1-5  to  1-7  the  grate  area. 

Note  the  condition  of  the  tubes  both  from  the  front  and 
back  connections. 


274  PRACTICAL  MARINE  ENGINEERING. 

Examine  the  dampers  in  uptakes  and  funnel  to  see  if  they 
are  in  working  order,  and  open  them  preparatory  to  lighting 
the  fires. 

Examine  carefully  all  valves,  cocks,  piping  and  connections 
and  make  sure  that  everything  is  connected  up  as  it  should  be, 
and  that  no  valves  are  open  which  should  be  closed  nor  closed 
which  should  be  open. 

See  that  no  waste  or  other  inflammable  substances  have 
been  left  about  by  workmen  on  the  tops  of  the  boilers. 

If  the  water  has  not  been  previously  run  up  in  the  boilers, 
this  may  be  under  way  in  the  meantime.  In  modern  practice 
the  boilers  are  always  filled  with  fresh  water  where  possible,  ob- 
tained from  a  hydrant  on  the  dock  or  water-boat  alongside,  and 
put  in  usually  by  a  hose  through  an  upper  manhole.  If,  how- 
ever, the  boat  is  lying  in  fresh  water,  or  if  by  necessity  the  water 
is  to  be  taken  from  overboard,  it  is  then  run  in  through  the  bot- 
tom blow  and  Kingston  valve.  In  the  meantime  examine  the 
connections  leading  to  the  water-gauge  and  cocks.  Clean  the 
glass  if  necessary,  and  make  sure  by  means  of  a  wire  that  the 
opening  through  the  cocks  is  clear.  The  packing  of  the  gauge 
glass  should  also  be  examined  and  renewed  if  necessary.  When 
the  water  appears  in  the  gauge  glass  and  shows  from  one-half  to 
two-thirds  full  in  each  boiler,  it  may  be  shut  off. 

All  open  manholes  may  then  be  closed,  and  the  boilers  are 
ready  for  the  fires. 

Notice  of  the  time  when  steam  is  required  should  have  been 
given  not  less  than  from  six  to  eight  hours  in  advance,  and 
many  engineers  prefer  a  still  longer  time  in  which  to  bring  along 
everything  into  working  condition.  With  hard  coal  a  certain 
amount  of  wood  is  necessary  in  starting  the  fires.  With  soft 
coal  less  wood  is  required,  and  if  necessary  oily  waste  may  be 
made  to  answer  the  purpose.  If  fires  are  up  in  the  donkey 
boiler  a  little  live  coal  may  be  taken  from  them  to  assist  in  start- 
ing. As  soon  as  the  fires  are  going  the  hydrokineters  are  put  on 
if  such  appliances  are  fitted.  In  some  cases  arrangements  are 
made  for  drawing  the  water  by  the  donkey  or  auxiliary  feed- 
pump from  the  bottom  of  the  boiler  by  the  bottom  blow  and  re- 
turning it  through  the  feed-pipe,  thus  producing  a  forced  or  as- 
sisted circulation.  Where  there  are  no  appliances  for  forcing  the 
circulation  during  this  period,  it  is  considered  good  practice  to 
light  first  the  fires  in  the  center  furnaces,  and  later,  by  one  or 


OPERATION,  MANAGEMENT  AND  REPAIR.  275 

two  hours,  those  in  the  wing  furnaces.  The  natural  circulation 
thus  produced  will  more  nearly  even  up  the  temperature  within 
the  boiler  than  if  all  fires  are  lighted  at  the  same  time.  After 
the  fires  are  fairly  going  the  funnel  or  uptake  dampers  may  be 
partly  closed  so  as  to  hold  the  fires  back,  and  bring  them  along 
at  a  moderate  gait  as  desired. 

While  the  boilers  are  thus  warming  up  and  before  steam  has 
formed,  a  last  look  may  be  given  to  the  boiler  mountings  and 
their  connections.  The  various  cocks  and  valves  should  be 
worked,  and  especially  the  stop  and  safety  valves,  in  order  to 
make  sure  that  none  are  jammed  or  in  any  way  out  of  order. 
The  oil  lamps  for  the  steam  and  water  gauges  may  also  be 
trimmed  and  lighted,  or  the  electric  bulbs  cleaned,  if  such  are 
provided. 

During  this  period  the  steam-pipe  drains  and  safety  valves 
are  usually  open  to  allow  of  the  escape  of  the  air  and  of  the  con- 
densed vapor  as  formed.  In  some  cases,  however,  the  safety 
valves  are  closed,  and  the  stop  valves  being  open,  the  air  and 
vapor  are  expelled  along  the  steam-pipe  and  through  the  engine, 
thus  beginning  the  process  of  warming  up.  Many  engineers, 
however,  prefer  to  keep  the  boiler  stop  valves  closed  until  steam 
is  formed,  and  to  discharge  the  air  through  the  safety  valve,  or 
in  some  cases  through  a  specially  fitted  air-cock.  If  steam  is 
already  up  on  some  of  the  boilers  or  if  there  is  no  auxiliary 
steam-pipe  and  the  pressure  from  the  donkey  boiler  is  on  the 
main  steam-pipe,  then  of  course  the  stop  valves  must  be  closed 
on  the  boilers  in  which  steam  is  being  raised,  and  they  must  re- 
main closed  until  the  pressure  on  the  boiler  is  equal  to  that  in  the 
steam-pipe.  In  opening  a  boiler  stop  valve  connecting  with  a 
pipe  in  which  there  is  no  pressure  the  following  precautions 
should  be  taken : 

(1)  The  pipe  should  be  thoroughly  drained  and  especial 
care  should  be  taken  that  there  are  no  sags,  bends  or  U's  un- 
provided with  proper  drains,  and  in  which  a  pocket  of  water  may 
have  collected. 

(2)  The  valve  should  be  very  carefully  eased  from  its  seat 
and  opened  only  from  a  quarter  to  a  half  turn  until  the  pipe  is 
under  full  boiler  pressure  and  has  taken  the  temperature  of  the 
steam,  and  the  drains  are  discharging  steam  instead  of  water. 
In  opening  a  boiler  stop  valve  connecting  with  a  pipe  in  which 
there  is  approximately  the  same  pressure  as  in  the  boiler,  it  is 


276  PRACTICAL  MARINE  ENGINEERING. 

simply  necessary  to  ease  the  valve  from  the  seat  and  note  by  the 
sound  whether  there  is  a  sufficient  difference  of  pressure  to  cause 
any  violent  flow  in  one  direction  or  the  other.  As  soon  as  the 
absence  of  such  evidence  indicates  an  equality  of  pressure  on 
both  sides  of  the  valve,  it  may  be  opened  out  as  desired. 

The  two  fundamental  principles  underlying  much  of  this 
routine  and  detail  are  simply  as  follows : 

(1)  To  prevent  as  far  as  possible  sudden  changes  in  the 
temperature  condition  of  the  boilers,  piping  and  machinery,  and 

(2)  To  prevent  throughout  the  steam-pipe  system  the  accu- 
mulation of  water  at  any  point. 

If  these  two  points  are  kept  clearly  in  view  and  good  en- 
gineering judgment  used  in  carrying  them  out,  the  life  of  the 
boilers  and  machinery  will  be  prolonged,  and  danger  of  ruptured 
pipes  through  the  effects  of  water  hammer  will  be  avoided. 

After  steam  is  formed  and  the  pressure  has  risen  to  some  40 
or  50  pounds  the  hydrokineters  may  be  shut  off,  especially  if  the 
ship  is  to  get  under  way  as  soon  as  ready.  If,  however,  the  boil- 
ers are  to  stand  some  time  with  steam  up,  it  may  be  advisable  to 
turn  on  the  hydrokineters  from  time  to  time,  at  least  as  long  as 
the  pressure  in  the  donkey  boiler  is  sufficient  for  the  purpose. 

The  fires  in  the  meantime  have  been  kept  simply  in  good 
condition  without  forcing,  and  even  if  they  work  under  a  forced 
draft  system,  only  enough  air  should  be  provided  during  this 
stage  to  bring  them  along  at  the  gradual  pace  which  will  allow 
the  boiler  to  properly  accommodate  itself  to  the  change  in  tem- 
perature and  other  conditions. 

The  fire-room  auxiliary  machinery  should  also  be  examined 
during  this  period,  and  tested  under  steam  from  the  donkey 
boiler  if  possible.  The  feed  pumps  should  first  receive  attention, 
in  order  that  there  mav  be  no  question  as  to  the  proper  supply  of 
feed-water  when  required. 

The  fan  engines  should  be  examined,  oiled  and  turned  over 
under  steam. 

The  ash-hoist  gear  and  engine,  or  ash  ejector  and  pump, 
should  be  examined  and  put  in  working  order. 

If  steam  for  these  purposes  is  not  to  be  had  from  the  donkey 
boiler,  then  as  soon  as  a  sufficient  head  is  formed  on  the  main 
boilers  these  auxiliaries  must  be  examined,  taking  in  all  cases  the 
feed  pump  first. 

Soon  after  lighting  fires  it  may  be  desirable  to  slacken  up 


OPERATION,  MANAGEMENT  AND  REPAIR.  277 

somewhat  on  the  funnel  guys  on  deck,  in  order  that  the  expan- 
sion of  the  funnel  may  not  bring  an  undue  stress  upon  the  guys 
and  their  connections,  or  upon  the  funnel  and  its  supports. 
After  the  ship  is  away  and  the  funnel  has  taken  its  temperature 
for  running  conditions,  the  guys  may  be  tightened  up  so  as  to 
properly  support  the  funnel  in  a  sea  way. 

[2]  Fire  Room  Routine. 

At  length  we  may  suppose  that  full  head  of  steam  has  been 
formed  on  the  boilers,  that  the  fires  have  been  brought  up  to 
proper  condition,  and  that  the  ship  has  gotten  under  way  for  the 
voyage.  As  soon  as  possible  the  operations  in  the  fire-room 
should  be  brought  to  a  regular  routine.  This  will  involve  the 
following  chief  features,  which  we  shall  consider  separately: 
(i)  Firing.  (2)  Water  tending.  (3)  Disposal  of  ashes. 
(4)  Cleaning  fires.  (5)  Sweeping  tubes. 

Firing. — The  routine  of  firing  should  be  so  arranged  that  no 
two  furnaces  in  boilers  connected  to  the  same  stack  shall  be  open 
at  the  same  time.  If  this  is  not  practicable,  then  care  must  be 
taken  to  avoid  at  least  firing  at  the  same  time  furnaces  in  oppos- 
ite ends  of  double-end  boilers,  especially  if  there  is  a  common 
combustion  chamber.  Two  furnaces  in  a  single-end  boiler,  or  in 
the  same  end  of  a  double-end  boiler  will,  of  course,  never  be 
fired  at  the  same  time.  It  is  now  well  understood  that  firing 
light  and  often  is  better  than  heavy  and  at  great  intervals. 
There  is,  however,  a  limit  to  this,  for  the  oftener  the  firing  the 
more  are  the  furnace  doors  open  and  the  more  is  the  draft  subject 
to  disturbance,  while  the  arrangement  of  a  suitable  routine  be- 
comes more  and  more  difficult. 

Light  and  frequent  firing,  especially  with  water-tube  boil- 
ers, is  now,  however,  the  rule  where  the  best  results  are  to  be 
obtained.  The  furnace  door  should  be  opened  smartly  and  kept 
open  only  the  minimum  time  needed  to  get  the  coal  on.  Hard 
coal  is  spread  in  as  even  a  layer  as  possible  over  the  grate.  For 
firing  soft  coal  two  methods  are  available.  When  firing  for  coal 
efficiency,  that  is  to  get  the  most  heat  out  of  a  pound  of  fuel, 
the  coal  should  be  first  charged  in  front  and  coked,  and  then 
should  be  pushed  back  and  burned.  When  firing  for  weight 
efficiency,  that  is  to  get  the  most  power  out  of  the  boiler,  the 
former  method  would  be  too  slow  and  the  coal  must  be  spread 
over  the  fire  and  burned  without  waiting  for  the  separate  dis- 


278  PRACTICAL  MARINE  ENGINEERING. 

tillation  and  combustion  of  its  gases.  Where  the  coal  runs  ir- 
regular in  size  the  large  lumps  should  be  broken  into  pieces  not 
larger  than  the  fist.  The  thickness  of  the  fires  varies  with  the 
conditions,  from  six  to  ten  or  twelve  inches,  or  even  thicker  un- 
der a  heavy  forced  draft.  With  a  given  speed  of  fan  the  air 
pressure  in  the  ash-pits  will  vary  widely  with  the  thickness  of 
the  fire,  rising  as  it  is  thicker,  and  falling  as  it  is  thinner  and  the 
air  finds  more  ready  passage  through.  With  a  thick  fire  it  will 
therefore  be  easy  to  get  a  strong  draft  pressure  in  the  ash-pits, 
while  with  a  thin  fire  it  will  be  perhaps  impossible,  even  with  a 
much  higher  speed  of  fan.  A  strong  draft  pressure  will  not, 
however,  produce  the  corresponding  rate  of  combustion  unless 
the  thickness  and  condition  of  the  fire  are  such  that  the  pressure 
is  able  to  drive  through  it  the  necessary  amount  of  air.  For  the 
best  combustion  the  thickness  of  the  fire  should  be  so  adjusted  to 
the  draft  pressure  that  the  latter  is  able  to  drive  the  necessary 
air  through,  and  keep  it  in  a  state  of  active  combustion  through- 
out from  fire  grate  to  upper  surface.  Care  must  be  taken  to 
keep  the  grates  evenly  covered,  especially  at  the  back,  and  to 
prevent  the  formation  of  relatively  thin  or  bare  spots.  A  spot 
which  is  relatively  thin  allows  of  the  passage  of  relatively  more 
air.  This  further  increases  the  combustion  at  that  point  and 
the  spot  becomes  still  thinner,  thus  allowing  more  and  more  air 
to  escape  freely  instead  of  passing  through  the  remainder  of  the 
fire  as  it  should. 

In  the  intervals  of  firing  the  pricker  and  slice  bars  may  be 
used  to  clear  away  the  ashes  and  clinker,  if  such  is  forming. 
Care  should  be  taken  to  prevent  the  formation  of  dull  or  dead 
spots  due  to  "the  accumulation  of  ashes  or  clinker,  especially  at 
the  corners  of  the  grate.  Among  old  firemen  a  familiar  saying 
relating  to  this  point  is :  "Take  care  of  the  corners  and  sides 
of  the  fire  and  the  middle  will  take  care  of  itself."  The  ash-pits 
should  also  be  kept  clear  of  ashes,  for  if  allowed  to  accumulate 
they  will  prevent  the  passage  of  air  to  the  grate,  especially  at  the 
back.  If  the  passage  of  air  is  thus  interfered  with  to  any  con- 
siderable extent  there  will  be  also  danger  of  overheating  the 
grates  and  of  bringing  them  down  into  the  ash-pits. 

In  connection  with  the  use  of  the  slice  bar,  it  must  not  be 
forgotten  that  every  opening  of  the  furnace  door  means  an  in- 
rush of  cold  air  into  the  furnace,  a  checking  of  the  draft,  a  distur- 
bance of  the  combustion,  and  often  severe  strains  on  the  struc- 


OPERATION,  MANAGEMENT  AND  REPAIR.  279 

ture  of  the  boiler,  due  to  the  sudden  chilling  and  contraction 
which  the  heating  surfaces  undergo.  If  shaking  grates  are  fitted 
much  of  this  cleaning  may  be  done  without  opening  the  door, 
though  no  form  of  grate  is  quite  able  to  deal  satisfactorily  with 
coal  showing  a  decided  tendency  to  form  clinker. 

In  thus  working  the  fires  a  certain  amount  of  fine  unburned 
or  partly  burned  coal  will  be  shaken  down  into  the  ash-pit.  In 
some  cases  this  forms  so  large  a  part  of  what  comes  through  the 
grate,  that  it  may  be  immediately  thrown  onto  the  fire  and 
burned  over  again.  In  most  cases  a  sifting  or  washing  of  the 
ashes  and  separation  of  the  combustible  from  the  non-combus- 
tible would  show  a  surprisingly  large  per  cent,  to  be  available  as 
fuel,  and  some  saving  could  usually  be  effected  in  this  way.  It 
is  rare,  however,  that  anything  of  the  kind  is  attempted,  as  with 
present  prices  of  coal  it.  may  be  doubted  whether  the  additional 
appliances  and  labor  would  be  paid  for  by  the  saving  effected. 

Water-tending.  The  care  of  the  water  is  the  most  important 
and  responsible  of  the  duties  in  the  fire-room.  The  ideal  is  to 
keep  the  water  regularly  flowing  inward  through  the  check- 
valves  at  about  the  same  rate  as  it  is  flowing  outward  as  steam 
through  the  steam  pipe.  This  requires  constant  watch  and  ad- 
justment of  the  valves,  closing  down  where  it  is  entering  too  rap- 
idly and  opening  up  where  it  is  entering  too  slowly.  Instead  of 
this  method  it  is  often  the  custom  to  put  the  feed  on  strong  first 
to  one  boiler  and  then  another,  in  order,  according  to  the  firing, 
feeding  the  boiler  up  when  the  fire  is  at  its  best,  and  shutting 
down  when  it  is  freshly  coaled.  The  steady  and  uniform  feed  is, 
however,  better  because  it  approaches  more  nearly  to  a  uniform 
condition  of  the  boiler,  especially  on  the  water  side. 

The  position  of  the  water  is  determined,  of  course,  from  the 
water  gauge  and  cocks.  It  is  necessary,  of  course,  that  the 
gauge  and  its  connections  be  clear  of  any  obstruction  in  order 
that  the  height  of  the  water  may  be  properly  indicated.  To  make 
sure  that  everything  is  clear  the  gauge  glass  and  connections 
are  blown  through  by  the  "double  shut  off"  method  as  follows : 
In  Fig.  203,  G  represents  the  glass,  A  the  drip  cock,  B  and  C  the 
cocks  connecting  to  the  stand,  and  D  and  E  those  connecting 
the  stand  to  the  boiler.  First,  B  and  E  are  closed,  and  A  is 
opened.  If  steam  blows  through  it  shows  that  A  G  C  D  are 
clear.  Second,  C  and  D  are  closed  and  A  is  opened.  If  water 
blows  through  it  shows  that  ABE  are  clear.  The  action  of  the 


280 


PRACTICAL  MARINE  ENGINEERING. 


water  in  the  glass  will  usually  show  to  an  experienced  eye 
whether  or  not  the  connections  are  clear.  If  the  water  is  lively 
and  follows  the  rolling  of  the  ship  it  is  a  good  indication  that  the 
passages  are  clear.  Otherwise  it  indicates  that  an  obstruction 
exists  which  must  be  sought  out  without  delay.  In  the  mean- 
time the  water  cocks  are  relied  upon,  and  in  fact  many  ex- 
perienced water  tenders  prefer  the  indications  of  the  cocks  to 
those  of  the  glass,  while  they  should  in  all  cases  be  freely  used 
as  a  check  on  the  glass.  To  those  without  experience,  however, 
the  glass  is  less  apt  to  be  misleading.  The  indications  of  the 


Fig.  203. 


Marine  Ziiyizeeriny 

Test  for  Water  Gauge  and  Glass. 


water  cocks  are  sometimes  difficult  to  interpret,  because  fre- 
quently it  is  not  easy  to  tell  whether  water  or  steam  is  blowing 
off.  With  high  pressure  steam  especially,  a  jet  of  water  issuing 
at  a  temperature  of  350  degrees  to  400  degrees  is  instantly  sur- 
rounded with  a  shell  of  vapor  formed  by  the  vaporization  of  part 
of  the  jet.  Furthermore, if  the  water  in  the  boiler  is  in  active  ebul- 
lition near  to  the  surface  so  that  the  jet  would  be  drawn  from  a 
mixture  of  steam  and  water,  then  on  issuing  it  becomes  practical- 
ly a  jet  of  moist  steam.  On  the  other  hand  if  the  water  is  well 
below  the  cock  so  that  the  jet  would  be  drawn  from  steam  alone 


OPERATION,  MANAGEMENT  AND  REPAIR.  281 

or  from  moist  steam,  then  on  issuing  it  will  become  dry  and 
usually  super-heated.  It  is  also  a  fact,  especially  with  water-tube 
boilers,  that  due  to  a  kind  of  lifting  action,  a  cock  will  often  dis- 
charge moist  steam  or  a  mixture  of  water  and  steam,  even  if  the 
water  level  is  somewhat  below  the  mouth  of  the  cock.  It  is 
hence  readily  seen  that  the  indications  from  the  cocks  must  be 
interpreted  with  judgment,  and  that  some  experience  is  neces- 
sary in  order  to  always  draw  correct  conclusions  from  them. 
It  is  often  difficult  to  distinguish  between  an  empty  glass  and 
one  entirely  full.  In  order  to  make  sure  close  the  cock  B,  Fig.  203, 
and  slightly  open  A.  If  the  gauge  is  full  of  water  the  surface 
will  gradually  descend,  first  coming  into  view  in  the  top  of  the 
glass  and  then  passing  out  of  view  at  the  bottom.  If  then  A  is 
closed  and  B  is  slightly  opened,  the  water  will  rise  again  in  the 
glass  and  pass  out  of  view  at  the  top. 

Blowing  off.  Blowing  off  boilers  to  reduce  the  concentra- 
tion or  density  of  the  water  is  now  rare  in  good  practice.  In- 
stead of  reducing  density  by  introducing  sea-water  for  feed  make 
up,  evaporators  are  installed  for  providing  fresh  water  make  up, 
or  for  short  runs  additional  fresh  water  is  often  carried  in  double 
bottoms  or  spare  tanks  provided  for  the  purpose. 

In  modern  practice  the  purpose  of  blowing  off  is  (i)  to  get 
rid  of  mud  or  slush  in  the  bottom  of  the  boiler  or  in  the  special 
mud  drums  of  a  water-tube  boiler,  and  (2)  to  get  rid  of  oil  and 
scum  at  and  near  the  surface  of  the  water.  For  the  former  a 
bottom  blow  or  special  mud  cock  is  required,  while  for  the  latter 
the  surface  blow  is  used.  In  ordinary  experience  on  deep  sea 
voyages  where  evaporators  or  other  fresh  water  make  up  is  pro- 
vided, the  use  of  the  surface  blow  is  all  that  is  needed  to  keep 
the  water  in  good  working  condition.  It  must  not  be  forgotten 
that  the  use  of  the  blow-off  means  a  direct  loss  of  heat,  and  hence 
it  should  be  used  with  discretion,  and  no  more  frequently  than  is 
needed  for  the  purpose  in  view.  An  idea  of  the  condition  of  the 
water  in  the  boiler  near  the  surface  may  be  obtained  by  drawing 
off  a  little  water  from  a  cock  fitted  into  the  surface  blow  pipe,  or 
from  a  gauge  cock  fitted  directly  to  the  boiler.  The  water  being 
allowed  to  cool  and  settle,  is  then  poured  into  a  glass  jar,  when 
its  condition  is  readily  noted,  and  the  need  of  using  the  blow 
determined. 

It  may  be  well  to  speak  at  this  point  of  the  proper  method  of 
testing,  from  the  outside,  the  correct  position  of  a  plug  cock  han- 


282  PRACTICAL  MARINE  ENGINEERING. 

die  for  "closed"  and  for  "open."  Instances  have  been  known 
where  there  was  no  mark  on  the  head  of  the  plug,  and  the  han- 
dle becoming  bent  or  being  wrongly  placed,  the  cock  was  left 
shut  when  it  was  supposed  to  be  open,  or  open  when  supposed 
to  be  shut,  with  the  possibility  of  most  serious  consequences, 
especially  in  the  latter  case. 

A  careful  examination  of  the  cock,  aided  if  need  be  by 
placing  the  ear  to  the  chamber,  will  suffice  to  tell  whether  or  not 
the  cock  is  open  and  water  or  steam  passing  through.  Then  the 
cock  being  open  let  it  be  turned  in  one  direction  until  it  is  just 
closed,  and  then  back  in  the  other  direction  until  it  is  closed 
again.  Half  way  between  these  two  positions  it  will  be  wide 
open,  and  at  right  angles  to  the  latter  position  it  will  be  full  shut. 

Taking  the  Saturation  or  Testing  the  Density  of  the  Water. — 
The  density  of  the  water  is  determined  by  the  use  of  a  hydro- 
meter or  salinometer  as  it  is  often  termed.  Under  modern  con- 
ditions where  evaporators  provide  fresh  water  make  up,  the 
density  rises  but  slowly,  and  it  is  usually  only  necessary  to  ob- 
serve its  value  once  or  twice  a  day.  It  is  usually  not  allowed  to 
rise  above  two  or  two  and  one-half.  See  Sec.  17  [10] . 

Disposal  of  Ashes. — For  the  disposal  of  ashes  two  chief 
means  are  in  use.  According  to  the  older  method  they  are  sent 
up  and  disposed  of  through  an  ash  chute  leading  overboard  and 
down  the  side  of  the  ship  to  the  water,  and  this,  method  is  still 
extensively  used  in  large  and  deep  ships.  In  the  more  modern 
system  they  are  disposed  of  from  the  fire-room  direct  by  means 
of  an  ash  ejector.  In  either  system  it  is  usually  sufficient  to 
dispose  of  the  ashes  once  in  a  watch,  and  they  are  collected,  wet 
down  and  either  hoisted  in  buckets  or  shoveled  direct  into  the 
ash  hopper  usually  between  6  and  7  bells. 

Cleaning  of  Fires. — The  routine  working  of  fires  spoken  of 
above  will  suffice  to  keep  them  in  fairly  good  condition  for  sev- 
eral hours,  provided  the  coal  is  of  fairly  good  quality.  It  usually 
becomes  necessary,  however,  to  give  to  each  fire  from  time  to 
time  a  more  thorough  cleaning  than  is  possible  in  the  manner 
previously  referred  to.  To  this  end  the  fire  should  be  taken 
when  partly  burned  down,  but  not  too  far  lest  there  be  nothing 
left  after  cleaning  on  which  to  build  up  again.  One  side  may 
be  cleaned  first,  working  the  good  coal  over  to  the  other  side, 
separating  out  the  clinker  and  ashes,  and  hauling  out  the  latter. 
Then  similarly  with  the  other  side,  working  the  good  coal  over  to 


OPERATION,  MANAGEMENT  AND  REPAIR.  283 

the  side  first  cleaned  and  pulling  out  the  clinker  and  ash.  The  live 
coal  is  then  spread  over  the  grates,  fired  lightly,  and  so  brought 
up  again  into  regular  conditions.  In  some  cases  there  is  so  little 
left  after  a  thorough  cleaning  that  live  coal  must  be  borrowed 
from  another  furnace  to  save  the  fire.  Only  judgment  and  ex- 
perience can  determine  the  best  point  at  which  to  clean  a  fire  so 
as  to  insure  the  minimum  loss  of  heat,  and  at  the  same  time 
have  enough  coal  left  to  nicely  build  on  again.  Some  engineers 
prefer  to  burn  the  fire  almost  completely  down  to  the  ashes  and 
clinker,  and  then  pull  the  entire  contents  of  the  grate  out  and 
start  afresh.  This  method,  however,  chills  the  furnace  and  more 
seriously  interferes  with  the  operation  of  the  boiler,  and  is  not  to 
be  recommended.  It  must  of  course  not  be  forgotten  that  heat 
is  lost  with  the  clinker  and  ashes  withdrawn,  and  the  general 
operation  should  be  so  conducted  as  to  keep  this  loss  down  to 
the  minimum  possible. 

Under  usual  conditions  the  fires  will  need  cleaning  in  this 
way  at  intervals  of  from  12  to  16  hours,  or  at  least  once  a  day. 

Sweeping  Tubes. — In  addition  to  the  cleaning  of  fires  the 
tubes  will  require  cleaning  from  time  to  time,  dependent  on  the 
character  of  the  coal  and  other  circumstances.  With  soft  coal 
and  moderate  draft  they  will  soon  become  partly  filled  with 
soot  and  ashes,  thus  choking  the  draft  still  further,  and  prevent- 
ing the  transfer  of  heat  to  the  water  through  the  metal  of  the 
tube. 

To  prepare  for  sweeping  tubes  the  draft  is  checked,  ash-pit 
doors  put  up,  furnace  doors  opened  and  front  connection  doors 
raised.  Care  should  be  taken  to  wait  until  the  fire  is  burned 
partly  down  before  doing  this,  so  that  the  circulation  of  air 
through  the  grates  may  not  be  shut  off  while  the  fires  are  too 
heavy,  thus  endangering  the  grate  bars.  For  cleaning  the  tubes 
the  ordinary  wire  tube  brush  may  be  used.  This  consists  of  a 
mounting  carrying  wire  bristles  and  fitted  usually  with  a  jointed 
handle  by  means  of  which  it  is  pushed  and  pulled  through  the 
tubes,  thus  cleaning  out  the  soot  and  ashes  collected  there. 
A  more  modern  method  consists  in  blowing  through  tfre  tubes 
with  a  steam  jet.  The  mounting  of  this  appliance  consists  of  a 
flange  or  conical  ring  fitting  closely  to  the  end  of  the  tube  and 
provided  with  a  steam  nozzle  directed  along  the  center  of  the 
tube.  A  handle  is  provided  for  holding  and  guiding  the  ap- 
paratus, and  steam  is  led  to  it  by  means  of  a  flexible  hose.  By 


284  PRACTICAL  MARINE  ENGINEERING. 

this  means  the  ashes  and  soot  are  driven  out  of  the  tubes  into 
the  combustion  chamber.  By  still  another  form  of  apparatus  the 
jet  is  not  directed  into  the  tube  but  across  the  front  end  pro- 
ducing a  suction,  and  thus  drawing  the  ashes  and  soot  to  the 
front  connection  and  discharging  them  up  the  funnel. 

The  operation  of  sweeping  tubes  is  one  that  is  necessary  to 
maintain  the  continued  efficient  operation  of  the  boiler,  but  it 
must  not  be  forgotten  that  it  involves  a  serious  disturbance  to 
the  draft  of  the  whole  battery,  that  the  chilling  of  the  heating  sur- 
faces and  interruption  to  the  regular  routine  are  hard  on  the 
boiler  itself,  and  that  hence,  it  should  only  be  done  when  neces- 
sary and  then  as  quickly  as  possible. 

Stopping  Suddenly. — With  everything  going  along  its  regu- 
lar schedule,  suppose  that  the  engine  is  suddenly  stopped.  The 
dispositions  to  be  taken  wrill  depend  on  whether  the  stoppage  is 
momentary  or  whether  it  is  expected  to  last  for  some  time.  Here" 
again  the  caution  regarding  a  sudden  change  in  the  conditions 
must  be  kept  in  mind.  If  the  stop  is  but  momentary  it  wifl 
probably  be  sufficient  to  shut  off  the  draft,  close  the  dampers  and 
put  on  the  feed  strong,  standing  by  to  ease  open  the  safety 
valves  in  case  the  pressure  rises  too  near  the  point  of  blow- 
ing off.  If  the  stop  is  to  be  longer  it  may  be  necessary  to  still 
further  check  the  fires  by  putting  up  the  ash  pit  doors  and  open- 
ing the  furnace  doors.  Caution  must  be  exercised  in  thus  check- 
ing the  flow  of  air  through  the  grates  lest  there  be  danger  of 
overheating  the  bars,  or  even  of  bringing  them  down  into  the  abh 
pit.  Of  these  various  steps  for  checking  the  fires  the  opening 
of  the  furnace  doors'  and  the  sudden  chilling  of  the  heating  sur- 
faces is  the  most  objectionable  and  should  not  be  resorted  to 
unless  necessary.  As  an  additional  means  the  fires  may  be 
freshly  coaled,  especially  with  dampened  coal.  This  will  check 
the  formation  of  steam  and  provide  fuel  for  bringing  them  into 
good  condition  for  the  next  start.  A  period  of  stoppage  like, 
this  may  also  be  taken  advantage  of  to  clean  such  fires  as  may 
be  in  need  of  it. 

In  addition  to  checking  the  formation  of  steam,  that  which 
is  formed  may  often  be  used  in  a  variety  of  ways.  If  evaporators 
are  provided  it  may  be  turned  on  to  them  and  thus  go  toward 
increasing  the  store  of  fresh  feed  water.  The  bilge  pump  may 
also  be  put  on  strong,  and  if  its  exhaust  is  saved  there  will  be 
no  loss  of  fresh  water.  In  some  cases  with  independent  air  and 


OPERATION,  MANAGEMENT  AND  REPAIR.  285 

circulating  pumps  a  bleeder  is  provided  for  taking  the  steam 
direct  from  the  main  steam  pipe  to  the  condenser.  Here  it  is 
condensed  and  then  sent  by  the  feed  pumps  back  to  the  boilers, 
thus  avoiding  blowing  off  at  the  safety  valves  and  the  loss  of 
fresh  water,  and  allowing  the  fires  to  be  gradually  reduced  to  the 
condition  desired  for  the  period  of  stoppage. 

Here  again  in  all  of  these  operations  general  principles  aro 
often  worth  more  than  a  multitude  of  minor  directions.  These 
principles  are  (i)  Sudden  chilling  of  the  boiler  heating  surfaces 
must  be  avoided  as  far  as  possible.  (2)  Fresh  water  in  the  form 
of  steam  should  not  be  wasted,  and  (3)  Care  must  be  taken  not 
to  allow  the  grate  bars  to  melt  down. 

So  far  as  relates  to  the  general  securing  of  the  machinery 
and  gear  in  the  fire-room,  the  hints  given  in  connection  with 
getting  under  way  will  be  a  sufficient  guide  in  reversing  the 
process. 

Supplementary  Hints  Relating  to  Water. Tube  Boilers. — In 
water-tube  boilers  the  circulation  is  usually  more  nearly  natural 
than  in  fire-tube  boilers,  and  circulating  devices  are  not,  there- 
fore, required.  Steam  may  be  raised  in  such  boilers  in  from 
twenty  minutes  to  one  hour,  depending  on  the  type,  character 
of  the  draft,  etc.  With  this  type  of  boiler  it  is  especially  neces- 
sary that  for  the  best  results  the  firing  be  light,  often  and  regu- 
lar, and  that  the  fires  be  kept  as  nearly  as  possible  in  a  uniform 
condition.  It  is  also  necessary  that  the  feed  be  regular,  and 
the  water  must  be  carefully  watched,  since  from  the  small  amount 
contained,  any  lack  of  feed  in  a  given  boiler  will  be  followed  by 
rapid  lowering  of  the  level,  and  by  a  rapidly  increasing  likeli- 
hood of  danger  to  the  tubes.  In  water-tube  boilers  it  is  es- 
pecially necessary  that  nothing  but  fresh  water  be  used  as  feed, 
and  great  care  must  be  taken  to  keep  the  condenser  tight  and 
the  fresh  water  make  up  ample  in  quantity. 

The  tubes  of  water-tube  boilers  become  coated  with  soot  and 
ashes  on  the  outer  or  fire  sjfie,  and  it  is  usually  a  very  difficult 
matter  to  satisfactorily  clean  them  without  the  use  of  a  steam 
jet.  In  continued  steaming  for  long  periods,  it  will  usually  be 
found  necessary  from  time  to  time  to  let  the  fires  die  down  some- 
what and  to  use  what  methods  are  available  for  blowing  off  and 
dislodging  the  soot  from  the  tubes. 

When  stopping  or  standing  by,  the  same  general  means  may 
be  adopted  as  in  fire-tube  boilers.     As  regards  injury  through 


286  PRACTICAL  MARINE  ENGINEERING. 

sudden  change  of  temperature,  the  water-tube  boiler  is  some- 
what less  liable  than  the  fire-tube.  This  is  due  to  the  nature  of 
the  construction  which,  especially  with  curved  or  built  up  ele- 
ments is  much  more  elastic  than  in  the  fire-tube  boilers.  It  is 
always  better,  however,  to  avoid  sudden  temperature  changes 
where  possible,  and  the  same  principles  may  be  properly  applied 
here  as  previously  discussed  in  reference  to  the  other  type  of 
boiler. 

Coming  Into  Port. — When  coming  into  port  notice  will 
usually  be  given  some  hours  in  advance,  so  that  the  fires  may 
be  worked  into  a  condition  in  accordance  with  their  expected 
disposition  after  arrival.  If  they  are  to  be  drawn  and  the  boilers 
opened  up  for  examination  and  repairs,  they  will  be  allowed  to 
burn  down  as  low  as  possible  so  as  to  use  no  more  fuel  than 
necessary,  and  to  leave  as  small  an  amount  as  possible  to  finally 
haul,  while  at  the  same  time  sufficient  steam  must  be  maintained 
to  bring  the  ship  safely  to  her  anchorage  or  dock.  If,  on  the 
other  hand,  the  fires  are  to  be  banked,  they  will  not  be  allowed 
to  burn  so  low.  It  may  be  recommended  to  bank  fires  on  the 
front  of  the  grates,  as  in  such  case  the  air  is  heated  as  soon  as 
it  enters  the  furnace  and  the  boiler  is  kept  at  a  more  nearly  even 
temperature  than  if  they  are  banked  at  the  back  of  the  grate. 
As  the  fires  are  banked  they  should  be  cleaned  and  enough 
fresh  coal  put  on  to  hold  them  in  the  condition  desired.  If  the 
fires  are  properly  managed  there  will  be  little  extra  steam  after 
the  engines  are  stopped,  and  this  may  be  readily  disposed  of  by 
means  of  the  evaporator,  bilge  pump,  bleeder,  safety  valve,  etc. 
Loss  of  fresh  water  at  this  time  is  of  course  less  objectionable 
than  when  on  the  voyage,  and  if  desired  the  steam  may  all  be 
blown  off  through  the  safety  valves.  Many  engineers,  however, 
object  to  using  the  safety  valves  and  escape  pipe  for  this  purpose 
except  as  a  last  resort,  and  prefer  other  means  as  mentioned.  In 
passenger  vessels  the  noise  occasioned  is  usually  considered  ob- 
jectionable, though  to  obviate  this  a  muffler  is  frequently  fitted 
in  the  escape  pipe. 

If  the  boilers  are  to  be  opened  fires  are  allowed  to  die  out  or 
are  hauled  immediately.  If  time  permits  the  former  plan  is  pref- 
erable, as  the  change  in  the  condition  of  the  boiler  is  more 
gradual.  When  the  fires  are  finally  hauled  and  the  furnaces,  back 
connections  and  tubes  cleaned  out,  the  ashes,  soot  and  clinker 
are  wet  down  and  piled  away  until  they  can  be  disposed  of  to 


OPERATION,  MANAGEMENT  AND  REPAIR.  287 

the  ash  barge,  as  few  harbor  regulations  allow  the  dumping  of 
ashes  overboard.  In  wetting  down  the  fires  after  they  are  hauled 
out  on  the  fire  room  floor,  or  in  wetting  down  ashes  at  any 
time,  care  should  be  taken  not  to  wet  the  fronts  of  the  boilers 
or  the  mouths  of  the  ash  pits.  The  local  chilling  will  not  im- 
prove the  quality  of  the  steel,  and  the  alternate  wetting  and  dry- 
ing will  increase  the  opportunities  for  surface  corrosion.  For  the 
same  reason  damp  ashes  should  never  be  piled  up  in  contact  with 
the  boiler  or  furnace  plates,  as  in  many  instances  serious  cor- 
rosion has  resulted  from  a  neglect  of  this  precaution. 

The  fires  being  burned  out  or  hauled,  some  engineers  pro- 
ceed to  blow  the  boilers  down  immediately.  This  plan,  however, 
cannot  be  recommended  and  should  not  be  adopted  unless  the 
time  available  for  examination  and  repairs  is  so  short  as  to  make 
it  absolutely  necessary.  It  is  far  better  to  let  the  steam  condense 
and  the  water  gradually  cool,  and  then  draw  it  out  by  means  of 
a  pump,  or  in  some  cases  run  it  into  the  bilge.  In  this  way  the 
boiler  cools  more  gradually  and  the  structure  is  left  in  better 
condition,  while  on  the  water  side  the  scale  and  incrustation  will 
usually  be  made  softer  and  more  easily  removed  than  when  the 
boiler  is  blown  down  with  steam  on. 

[3]  Emergencies  and  Casualties. 

(i)  Foaming  and  Priming. — These  terms  refer  to  a  disturbed 
condition  of  the  water  in  the  boiler,  of  such  a  nature  that  the 
water  level  is  more  or  less  uncertain  in  location,  and  the  steam 
space  is  partially  filled  with  foam  or  a  mixture  of  foam  and  water. 
In  severe  cases  of  foaming,  steam  seems  to  be  given  off  from 
almost  the  entire  mass  of  water  in  the  boiler,  causing  it  to  rise 
bodily  as  foam  and  water  and  fill  the  whole  steam  and  water 
space,  thence  entering  the  steam  pipe  and  passing  on  to  the 
engine.  In  other  cases  the  water  seems  occasionally  to  rise  in 
gulps,  nearly  unmixed  with  steam,  and  entering  the  steam  pipe 
pass  on  to  the  engine.  The  terms  foaming  and  priming  are  often 
used  as  meaning  practically  the  same  thing.  Where  a  difference 
is  implied,  foaming  is  understood  to  apply  more  especially  to 
the  uplifting  of  the  mixed  steam  and  water  as  foam,  while  prim- 
ing may  refer  more  particularly  to  the  lifting  of  water  as  such, 
and  its  passage  over  into  the  engine.  There  is,  however,  no 
clear  line  of  distinction  between  the  two  kinds  of  disturbances, 
and  there  are  all  grades  intermediate  between  the  extremes. 


288  PRACTICAL  MARINE  ENGINEERING. 

Foaming  may  be  due  to  the  presence  of  certain  forms  of  oil 
or  grease,  or  to  the  excess  of  soda  used  for  scale  prevention,  or 
to  other  impurities  in  the  water,  or  to  the  demand  for  steam 
too  large  in  proportion  to  the  steam  space  in  the  boilers.  A  sud- 
den change  in  the  character  of  the  feed  water  may  also  produce 
foaming.  In  former  days  when  jet  condensers  were  in  common 
use,  boilers  were  liable  to  foam  in  passing  from  sea  water  to 
fresh  water,  especially  if  the  latter  was  muddy,  and  again  in 
passing  from  fresh  water  back  to  sea  water.  In  modern  prac- 
tice foaming  is  due  either  to  the  presence  of  oil,  or  to  the  extreme 
demand  for  steam  from  the  boiler.  In  the  former  case  the  oil 
must  be  removed  from  the  boiler  by  a  free  use  of  the  surface 
blow,  and  kept  out  by  a  proper  filter.  In  the  latter  case  the 
engine  must  be  slowed  and  the  demand  for  steam  reduced  to  an 
amount  which  the  boiler  can  supply  without  the  danger  of  such 
disturbance. 

As  a  result  of  foaming  the  engine  slows  down,  power  and 
speed  are  lost,  while  due  to  the  possible  inability  of  the  relief 
valves  to  handle  all  of  the  water  coming  into  the  cylinders,  there 
may  be  serious  danger  of  breakdown.  There  is  also  danger  to 
the  boiler  in  foaming,  because  the  water  level  cannot  be  known 
with  certainty,  and  plates  or  tubes  may  become  overheated,  with 
danger  of  collapse  and  rupture.  The  tendency  to  foam  is,  there- 
fore, a  symptom  of  serious  import,  and  no  steps  should  be  neg- 
lected to  discover  and,  if  possible,  to  remove  the  cause. 

(2)  Feed,  Pump. — In  modern  practice  an  auxiliary  feed-pump 
is  always  provided  except  perhaps  in  very  small  craft.  If  then 
the  main  feed-pump  refuses  to  work,  the  auxiliary  pump  must 
be  brought -into  use  while  the  other  is  under  examination. 

The  chief  causes  which  may  disturb  the  operation  of  a  feed- 
pump are  the  following : 

(a)  Jamming  of  check  valve  or  other  closure  in  the   de- 
livery pipe. 

(b)  Water  in  the  steam  cylinder. 

(c)  Derangement  or  sticking  of  the  steam  valves. 

(d)  Jamming  or  sticking  of  the  water  or  steam  plunger  in 
its  cylinder. 

In  addition  to  these  causes  which  may  affect  or  prevent  the 
motion  of  the  pump,  the  following  causes  may  prevent  it  from 
throwing  water  into  the  boiler,  even  though  its  movement  may 
be  entirely  regular : 


OPERATION,  MANAGEMENT  AND  REPAIR.  289 

(e)  Split  in  the  feed-pipe,  or  valve  open,  allowing  the  escape 
of  the  water  at  some  unexpected  point. 

(f)  Excessive  wear  of  water  plunger. 

(g)  Split  or  leak  admitting  air  on  the  suction  side  or  into 
the  suction  pipe. 

(h)  An  excessively  high  temperature  of  the  feed  water. 

(i)     Derangement  of  the  suction  or  discharge  valves. 

To  make  sure  that  the  delivery  pipe  is  free,  one  or  more 
feed-checks  and  the  air-cock  on  the  pump  may  be  opened.  If 
there  is  no  movement  of  the  pump  or  no  discharge  from  the 
cock  it  may  be  concluded  that  the  trouble  is  located  elsewhere. 

The  drain  valves  in  the  steam  cylinder  should  then  be  blown 
out  freely,  and  if  there  is  still  no  inclination  to  start,  the  trouble 
is  presumably  with  the  valve  gear. 

A  fresh  supply  of  oil  should  be  admitted  to  the  valve-chest, 
and  an  attempt  may  be  made  to  work  the  tappets  or  other 
valve  mechanism  by  hand.  In  many  cases  this  will  suffice  to 
start  the  pump  off  at  its  regular  gait.  If  it  does  not,  the  chances 
are  that  the  trouble  is  more  serious,  involving  the  stopping  up 
or  clogging  of  some  of  the  auxiliary  ports  or  passages,  or  the 
sticking,  jamming  or  excessive  wear  of  some  part  of  the  valve- 
gear.  A  removal  of  the  bonnets  and  complete  overhaul  can 
alone  lead  to  a  discovery  of  the  difficulty  in  such  cases. 

The  jamming  or  rusting  of  the  steam  or  water  plungers  in 
their  cylinders  could  only  result  from  long  disuse  and  gross 
neglect,  and  can  hardly  be  considered  as  of  likely  occurrence  in 
routine  work. 

If  the  feed-pump  is  working  properly  and  throwing  water 
into  the  boiler,  the  chamber  of  the  check-valve  will  be  relatively 
cool,  there  will  be  a  click  as  the  valve  rises  and  falls,  the  air  cock 
at  the  pump  will  show  a  stream,  and  the  water  will  rise  in  the 
boiler  gauge  glass.  At  the  same  time  an  experienced  eye  and 
ear  will  detect  by  the  manner  of  the  pump,  by  the  way  it  moves 
and  by  the  character  of  the  sounds,  whether  or  not  it  is  throwing 
water.  If  then  the  pump  works,  but  does  not  seem  to  be  throw- 
ing water,  we  must  have  resources  to  causes  such  as  those  men- 
tioned in  (e)-(i). 

There  are  here  two  chief  questions  to  be  answered.  First,  is 
the  pump  getting  water?  and  second,  if  it  is,  where  is  it  going? 
The  air  cock  will  usually  serve  to  answer  the  first  question.  If 
water  appears  here,  and  if  the  pump  shows  by  its  action  that  it 


29o  PRACTICAL  MARINE  ENGINEERING. 

is  handling  water,  it  is  evident  that  there  must  be  escape  at  some 
unexpected  point.  The  feed-pipe  must  then  be  carefully  ex- 
amined for  leaks,  and  all  valves  or  connections  leading  to  or  from 
it  should  be  examined  to  make  sure  that  the  water  is  not  escap- 
ing in  some  such  way.  In  one  case  coming  under  the  author's 
notice  the  main  feed-pipe  was  fitted  with  a  small  branch  leading 
to  the  forward  tank.  This  branch  was  closed  off  from  the  feed- 
pipe by  a  globe  valve.  Due  to  the  ignorance  or  carelessness  of 
some  attendant,  this  valve  was  jammed  wide  open  instead  of 
being  jammed  hard  shut.  At  low  or  moderate  pressure  the  feed- 
pump would  throw  enough  water  to  feed  the  boiler  in  spite  of 
this  leak.  The  trouble  was  therefore  not  discovered  until  a  full 
power  run  being  started,  the  demand  for  water  was  greater  and 
the  leakage  as  well,  so  that  the  boiler  was  soon  short  of  water, 
and  the  run  was  lost. 

If  no  trouble  is  found  in  the  feed-pipe,  the  difficulty  may  be 
sought  in  a  very  loosely  fitting  or  badly  worn  water  plunger. 
Such  a  plunger  will  discharge  water  into  the  air  or  even  against 
a  low  boiler  pressure,  but  may  not  be  able  to  force  it  against  the 
regular  pressure  in  the  boiler. 

If  from  the  evidence  of  the  air  cock  and  general  behavior 
of  the  pump  it  is  evident  that  no  watef  is  being  handled, 
the  suction  pipe  and  plunger  rod  packing  should  be  examined 
for  air  leaks. 

Where  there  is  some  considerable  lift  from  the  hot  well  to 
the  feed-pump,  an  unusually  high  temperature  of  feed-water,  on 
account  of  the  vapor  formed,  will  sometimes  prevent  the  pump 
from  taking  water.  In  good  practice,  of  course,  the  hot-well  is 
above,  or  at  least  not  below  the  feed-pump,  so  that  this  difficulty 
is  not  likely  to  arise.  If  such  should  prove  to  be  the  trouble  the 
feed-water  must  be  cooled  and  the  difficulty  will  be  removed. 

If  none  of  these  causes  seem  to  explain  the  failure  to  draw 
or  discharge  water,  then  the  trouble  is  probably  to  be  found  in 
the  suction  or  discharge  valves,  and  the  necessary  bonnets  or 
covers  must  be  removed  to  allow  of  their  examination. 

In  any  search  for  the  cause  of  the  trouble  in  the  feed-pump, 
the  details  may,  of  course,  be  modified  according  to  the  circum- 
stances, and  the  above  suggestions  are  more  especially  intended 
to  illustrate  the  principle  that  in  such  a  search  the  trouble  has 
often  to  be  found  by  a  continued  elimination  of  one  thing  after 
another,  taking  those  which  are  most  readily  examined,  and  thus 


OPERATION,  MANAGEMENT  AND  REPAIR.  291 

localizing    the    difficulty  as  quickly  and  as  readily  as  possible. 

(3)  Check-Valve  Jammed. — If  the  feed-pump  seems  to  be  in 
proper  condition  except  that  it  slows  down  and  stops  when  out- 
lets excepting  a  particular  check-valve  are  closed,  if  furthermore 
the  check-valve  chamber  is  hot,  there  is  no  click,  and  the  water 
does  not  rise  in  the  glass,  we  may  conclude  that  the  check-valve 
is  jammed  on  its  seat.    In  former  years  this  was  sometimes  due 
to  unequal  expansion  of  the  valve  and  seat,  and  nipping  of  the 
former  by  the  latter.    In  modern  practice  with  good  design  and 
an  angle  of  valve  seat  not  steeper  than  45  degrees,  such  an  oc- 
currence is  very  rare.    The  valve  may  also  become  jammed  by 
the  bending  or  other  derangement  of  the  stem  or  wing  guides, 
or  by  the  lodging  of  some  foreign  body  within  the  chamber.  If  the 
trouble  is  due  simply  to  unequal  expansion  the  usual  treatment  is 
to  wrap  the  valve  chamber  in  waste  or  clothes,  and  then  to  pour 
on  cool  water,  thus  reducing  the  temperature.    At  the  same  time 
the  chamber  may  be  tapped  near  the  valve  seat  with  a  hammer 
or  bar.    In  any  ordinary  case  of  sticking  due  to  unequal  expan- 
sion the  result  will  be  to  free  the  valve  from  its  seat.   If  this  does 
not   avail,   then   the    stop-valve   between   the    check-valve    and 
boiler  must  be  closed  and  the  check-valve  cover  removed,  so  as 
to  allow  an  examinaton  of  the  interior.     In  good,  modern  prac- 
tice at  least  two  check-valves,  main  and  auxiliary,  are  provided 
for  each  boiler,  so  that  there  should  be  no  danger  of  low  water. 
If,  however,  only  one  check  is  provided,  or  if  there  is  any  ques- 
tion of  shortness  of  water  while  the  necessary  repairs  are  being 
made,  the  stop-valve  should  be  closed  to  stop  the  draft  of  steam 
and  the  usual  precautions  taken  when  stopping  suddenly.     (See 
[2]  above). 

(4)  Bursting  of  Water  Gauge  Glass. — This  occurrence  is  by 
no  means  uncommon,  and  under  ordinary  circumstances  is  of 
relatively  small  importance.    With  the  type  of  gauge  glass  fitting 
having  self-closing  valves,  as  described  in  Sec.  17  [8],  the  flow 
of  water  and  steam  is  automatically  shut  off  and  the  new  glass 
is  readily  put  in.     Without  such  provision  the  shut-off  valves 
must  be  shielded  from  the  discharge  in  the  manner  most  readily 
effective,  and  then  quickly  closed.    In  setting  a  new  gauge  glass 
care  should  be  taken  to  see  that  the  fittings  are  well  lined  up, 
so  that  when  screwed  down  there  will  be  no  bending  strain  on 
the  glass.    If  any  pronounced  strain  is  thus  set  up  on  the  glass 
by  the  fitting,  it  will  be  almost  sure  to  break  in  a  short  time. 


29a  PRACTICAL  MARINE  ENGINEERING. 

The  packing  rings  should  also  be  screwed  down  no  tighter  than 
barely  sufficient  to  keep  the  joint  tight.  To  make  the  closing 
of  the  supply  valves  as  short  a  job  as  possible,  in  case  it  should 
become  necessary,  it  may  be  recommended  to  open  them  only 
enough  to  insure  a  good  supply  of  steam  and  water  to  the  glass, 
rather  than  wide  open.  Two  turns  of  the  valve  will  be  usually 
sufficient,  and  it  is  then  much  more  quickly  closed  than  when 
open  five  or  six  turns. 

(5)  Low  Water. — The  occurrence  of  low  water  or  the  ab- 
sence of  water  from  the  gauge  glass  is  one  of  the  most  serious 
emergencies  which  can  arise  in  the  fire-room.  Immediate  ac- 
tion is  called  for,  and  the  most  serious  consequences  may  result 
from  a  mistake,  or  indeed  may  result  in  spite  of  whatever  may 
be  done. 

If  there  is  reason  to  believe  that  the  water  has  but  just  dis- 
appeared from  the  glass  and  the  lower  gauge  cock  gives  indica- 
tions of  water  or  of  very  moist  steam,  it  may  be  fairly  assumed 
that  the  level  of  the  water  is  not  below  the  tubes  or  combus- 
tion chamber  tops,  and  in  such  case  there  will  be  no  immediate 
danger  of  overheating  or  collapse,  at  least  so  far  as  the  level  of 
the  water  is  concerned.  The  feed  may  therefore  be  put  on 
strong  without  hesitation,  and  if  the  diagnosis  has  been  correct 
the  water  will  soon  reappear  in  the  glass  and  the  incident  is  at 
an  end.  It  may  be  considered  prudent,  however,  to  check  at  the 
same  time  the  draft  of  steam  from  the  boiler,  and  to  deaden  the 
fires  to  some  extent  by  some  of  the  methods  referred  to  below. 
When  the  water  reappears  the  boiler  can  then  be  put  on  its 
regular  work  as  before. 

In  the  more  serious  case  when  the  location  of  the  water  is 
quite  unknown  and  the  gauge  cocks  and  glass  give  no  indica- 
tions, there  is  some  diversity  of  opinion  as  to  the  best  procedure. 
The  chief  point  of  difference  relates  to  the  propriety  of  imme- 
diately putting  on  a  strong  feed.  It  has  been  claimed  that  if 
the  plates  were  red  hot,  so  much  steam  would  be  suddenly  gen- 
erated as  to  rapidly  increase  the  pressure,  and  burst  the  boiler. 
On  the  other  hand,  it  has  been  pointed  out  that  the  amount  of 
steam  which  can  be  thus  formed  is  in  reality  comparatively 
small,  and  that  its  formation  cannot  be  instantaneous,  nor  even 
especially  rapid,  since  its  formation  will  extend  over  the  period 
while  the  water  is  rising  over  the  heated  surfaces.  In  no  way 
then  could  any  great  amount  of  steam  be  generated  with  es- 


OPERATION,  MANAGEMENT  AND  REPAIR.  293 

pecial  rapidity,  and  it  is  hard  to  see  how  its  formation  could 
take  place  more  rapidly  than  would  be  provided  for  by  the 
natural  outflow  to  the  engine,  and  by  the  safety-valve,  if  need 
arose.  To  obtain  some  definite  information  on  these  points,  ex- 
periments were  carried  out  by  a  Steam  Boiler  Insurance  Com- 
pany some  few  years  ago,  in  which  the  plan  of  putting  in  cold  feed 
upon  overheated  plates  was  followed.  The  boiler  could  not  be 
burst  by  the  operation,  and  no  very  pronounced  elevation  of 
pressure  was  produced.  So  far  as  the  results  of  these  experi- 
ments went,  it  would  seem  to  be  safe  to  put  on  the  feed  imme- 
diately in  such  an  emergency  as  we  are  now  discussing.  This 
conclusion  seems  also  to  be  borne  out  by  the  results  of  such 
practical  experience  as  is  obtainable.  There  are,  however,  dif- 
ferences of  opinion  on  this  point,  and  while  the  author  would 
follow  this  plan  in  such  a  case,  it  should  not  be  denied  that 
many  good  authorities  would  consider  it  unwise,  at  least  in  the 
earliest  stages  of  the  measures,  to  be  taken. 

Aside  from  getting  the  feed  into  the  boiler  as  soon  as 
prudence  will  permit,  the  other  great  point  is  to  deaden  the  fire. 
If  the  heating  surfaces  have  not  collapsed  when  the  condition  is 
discovered,  it  is  hardly  likely  that  the  plates  can  be  at  more  than 
a  very  dull  red,  and  if  the  supply  of  heat  can  be  effectually 
checked,  further  trouble  may  be  averted. 

To  this  end  a  plan  often  followed,  especially  in  former 
years,  was  to  haul  the  fires.  This,  however,  seems  very  unwise 
indeed.  While  being  hauled  the  fires  will  burn  up  all  the  more 
fiercely,  and  for  a  few  moments  the  heat  supply  will  be  in- 
creased rather  than  decreased.  Instead  of  hauling  directly, 
some  engineers  prefer  to  have  the  fires  dumped  into  the  ash-pits 
by  dislodging  a  few  grate-bars,  and  then  to  haul  from  there. 
This  plan  seems  but  little  better  than  the  other,  and  in  any 
event  the  immediate  result  will  be  to  increase  the  amount  of  heat 
given  off  at  the  very  time  when  it  should  be  decreased. 

A  far  better  plan  seems  to  be  to  deaden  the  fire  with  either 
moist  ashes  or  coal.  If  a  pile  of  wet  ashes  is  at  hand  they  should 
be  thrown  immediately  on  the  fire,  and  will  be  found  a  most 
effective  means  of  deadening  the  burning  coals.  In  default  of 
wet  ashes,  wet  or  even  dry  coal  may  be  thrown  on  and  the  fir$ 
simply  smothered.  At  the  same  time  the  dampers  should  be  put 
up  and  furnace  doors  left  open,  thus  checking  all  draft  and 
stopping  the  formation  of  heat. 


294  PRACTICAL  MARINE  ENGINEERING. 

As  between  these  two  operations,  the  deadening"  of  the  fire 
and  the  getting  in  of  feed-water,  the  author  is  of  the  opinion 
that  the  deadening  of  the  fire  is  of  the  more  immediate  impor- 
tance, and  should  be  attended  to  first,  because  it  will  produce 
the  most  immediate  effect  over  the  whole  heating  surface,  and 
will  serve  most  effectually  to  rapidly  check  the  further  heating 
of  the  plates.  Putting  in  the  feed  water  will  then  complete  the 
cooling,  but  the  direct  operation  is  slower,  and  more  local  in  its 
influence,  and  is  therefore  of  relatively  less  importance. 

In  all  such  emergencies  much,  of  course,  will  depend  on 
the  special  circumstances,  but  if  the  two  principles  be  kept  in 
view  that  the  fire  must  be  deadened  and  the  water  restored,  the 
details  may  be  left  to  good  engineering  judgment  to  execute. 

After  the  water  has  again  appeared  in  the  glass,  and  if  no 
ill  effects  seem  to  have  resulted  to  the  boiler,  the  fire  may  be 
again  gotten  into  condition  and  the  boiler  put  on  its  regular 
routine.  If,  however,  there  be  any  doubt  whatever  regarding 
the  possible  results  to  the  boiler,  no  chances  should  be  taken, 
but  the  boiler  should  be  disconnected  from  the  others,  the  safety- 
valve  raised  and  the  steam  blown  down,  while  the  fires  should 
be  hauled  or  allowed  to  die  out  and  the  boiler  allowed  to 
cool  down.  It  should  then  be  carefully  examined  for  symp- 
toms of  distress  or  collapse,  and  if  any  such  are  found  they  must 
receive  proper  attention  before  the  boiler  is  again  set  to  work. 

(6)  Collapse  of  Furnace  Crounis  or  Combustion  Chamber 
Plates. — The  collapse  of  a  part  of  the  heating  surface  is  due  either 
to  an  overheating  of  the  plates  or  tubes,  or  to  a  gross  error  in 
the  design.  We  may  dismiss  the  latter  as  not  liable  to  occur  in 
good  practice.  Overheating  may  result  from  either  low  water, 
or  from  a  coating  of  scale  or  of  oil  and  scale  on  the  water  side. 
In  the  former  case  with  no  water  to  absorb  the  heat  the  natural 
result  is  an  overheating  of  the  plate  until  it  becomes  red  hot, 
followed  by  its  collapse  and  rupture.  When  the  overheating  is 
due  to  the  presence  of  a  coating  of  scale,  the  gradual  bulge  or 
start  toward  a  collapse  may  result  in  cracking  off  the  coating 
and  in  letting  in  the  water  to  the  plate.  This  will  cool  the 
metal,  restore  its  strength,  and  thus  put  an  end  to  the  operation. 
In  some  cases  when  the  covering  is  a  mixture  of  scale  and 
oil,  the  overheating  of  the  plate  will  result  in  burning  off  or 
volatilizing  the  oil,  leaving  the  scale  as  a  fine  powdery  deposit. 
This  readily  admits  the  water  to  the  plate,  and  thus  the  metal 


OPERATION,  MANAGEMENT  AND  REPAIR.  295 

may  be  cooled  and  restored  in  strength,  and  further  bulging 
prevented.  This  nice  adjustment  of  heating,  burning  or  crack- 
ing off,  cooling  and  re-strengthening  before  final  rupture,  does 
not,  however,  always  occur.  Before  the  re-cooling  is  effected 
rupture  only  too  often  results,  and  the  contents  of  the  boiler 
are  more  or  less  completely  emptied  into  the  fire-room,  with 
consequences  always  severe  and  sometimes  fatal. 

If  it  is  discovered  that  the  furnace  crowns  have  come  down, 
but  without  final  rupture,  or  if  any  portion  of  the  heating  sur- 
face has  suffered  collapse  or  bulging,  but  without  final  rupture, 
it  may  be  assumed  that  the  overheating  was  due  to  scale  or  oil, 
and  that  the  change  of  form  or  the  overheating  has  resulted  in 
getting  rid  of  the  coating,  and  in  readmitting  the  water  to  the 
plate.  So  that  if  rupture  has  not  yet  occurred,  it  is  probable 
that  the  plate  is  safe  for  the  time  being,  and  in  such  case  the 
fire  may  be  first  deadened  and  then  hauled,  the  boiler  shut  off 
from  the  others  and  allowed  to  cool  down,  and  then  examined 
as  to  the  nature  and  extent  of  the  injury  sustained. 

(7)  Collapse  and  Rupture  of  Furnace  Crowns  or  Combustion 
Chamber  Plates. — In  the  event  of  rupture  following  upon  col- 
lapse, the  chief  thought  after  the  safety  of  human  life  must  be 
for  the  remaining  boilers  while  the  fire-room  is  in  such  condi- 
tion that  it  cannot  be  entered. 

The  general  nature  of  the  steps  which  may  be  taken  in  such 
case  are  discussed  in  the  following  section,  and  while  naturally 
judgment  must  be  depended  on  for  many  details,  it  is  readily 
seen  that  the  two  main  points  are  as  follows : 

(1)  To  isolate  the  injured  boiler. 

(2)  To  safeguard  the  remaining  boilers  from  injury  due  to 
low  water. 

(8)  Serious  Leakage  in  Boiler  Tubes. — A  serious  leak  may 
suddenly  develop  in  one  or  more  of  the  tubes.     A  split  in  the 
metal,  a  collapse  due  to  overheating,  or  perforation  due  to  deep 
pitting  or  general  corrosion  may  give  rise  to  such  an  occurrence. 
If  the  hole  or  holes  are  not  too  large  the  immediate  conse- 
quence will  not  extend  beyond  a  more  or  less  complete  filling  of 
the  fire  side  of  the  boiler  with  water  and  steam,  and  a  more  or 
less  pronounced  checking  or  deadening  of  the  fire.     In   such 
case  the  feed  should  be  looked  after  to  see  that  the  water  does 
not  get  low  in  the  boiler,  while  preparations  are  made  for  plug- 
ging the  tubes.    For  this  purpose  a  tube  stopper  or  plug  is  used, 


296  PRACTICAL  MARINE  ENGINEERING. 

of  which  there  are  many  varieties.  A  standard  type  of  stopper 
consists  of  two  heads  or  tapered  plugs  which  make  a  joint 
within  or  against  the  ends  of  the  tube,  and  are  held  in  place  by  a 
rod  running  through  the  tube,  threaded  at  the  ends  and  pro- 
vided with  nuts  for  holding  them  up  to  their  position  against 
the  ends  of  the  tube.  To  fit  this  stopper  it  is  necessary 
to  enter  the  combustion  chamber  to  adjust  the  back  end,  but 
once  properly  fitted,  it  may  be  depended  upon  to  fulfil  its  pur- 
pose. There  are  also  special  forms  of  tube  stoppers  which  may 
be  inserted  and  adjusted  from  the  front  end  only.  It  is  more 
difficult  to  make  a  tight  joint  with  the  latter  than  with  the  former 
stopper,  but  they  can  be  fitted  without  drawing  the  fire,  and 
therefore  in  an  emergency  may  prove  of  great  value.  Plugs  of 
soft  pine  are  also  used  for  temporary  purposes.  These  are 
pushed  in  from  the  front  until  they  cover  the  leak,  and  the  ex- 
pansion due  to  soaking  with  hot  water  is  depended  on  to  make 
a  tight  joint.  See  also  Sec.  42  [7]. 

If,  however,  the  holes  in  the  tubes  are  of  considerable  size, 
so  great  a  quantity  of  water  and  steam  may  be  liberated  as  to 
make  it  impossible  to  remain  in  the  fire-room.  In  such  case 
the  fire  will  usually  be  put  out  as  well,  or  at  least  so  deadened 
that  no  further  danger  of  collapse  due  to  overheating  need  be 
feared,  even  should  th>  water  become  low  in  the  boiler.  The 
general  safety  of  the  boiler  itself  is  thus  secured,  but  the  other 
boilers,  connected  through  the  main  steam  pipe,  will  continue 
pouring  out  their  steam  through  this  leak,  and  as  long  as  this 
condition  continues  it  will  thus  remain  impossible  to  return  to 
the  fire-room  to  attend  to  the  other  boilers.  The  first  care  after 
escaping  from  the  fire-room,  or  before  effecting  escape,  if  pos- 
sible, should  be  to  close  the  stop  valve  which  connects  the  boiler 
to  the  others,  and  thus  to  localize  the  trouble  to  the  one  boiler. 
If  the  stop  valves  are  arranged  so  as  to  be  worked  from  the 
deck  above,  as  is  frequent  in  good  modern  practice,  this  may 
be  readily  accomplished.  If  at  the  same  time  the  safety  valve 
on  the  injured  boiler  can  be  opened,  the  pressure  will  soon  be 
blown  down,  and  with  good  ventilation  from  the  fire-room  it 
will  be  possible  in  a  short  time  to  re-enter  it  and  give  the  needed 
attention  to  the  other  boilers.  In  the  meantime  also,  the  en- 
gines may  be  slowed  down  so  as  to  reduce  the  demand  for 
steam. 

Where  the  feed-pump  is  located  in  the  engine  room,  it  will 


OPERATION,  MANAGEMENT  AND  REPAIR.  297 

be  possible,  if  the  checks  have  been  left  open  on  the  other 
boilers  and  closed  on  the  injured  boiler,  to  feed  by  judgment  at 
a  rate  which  will  keep  these  boilers  safe  from  all  danger  of  low 
water.  The  object  of  these  various  steps  is,  of  course,  to  isolate 
the  injured  boiler  and  safeguard  it  from  anything  more  serious, 
and  to  provide  for  the  safety  of  those  remaining ;  and  while  cir- 
cumstances may  alter  the  details  of  the  measures  which  should 
be  taken,  the  above  suggestions  will  serve  to  illustrate  the  main 
points  to  be  looked  after. 

When  return  to  the  fire-room  is  possible,  and  after  the  other 
boilers  have  received  the  necessary  care,  attention  may  be  given 
to  the  injured  boiler;  the  fires  may  be  hauled,  and  after  cooling 
down,  the  nature  and  extent  of  the  damage  investigated. 

(9)  Rupture  of  Steam  Pipe. — In  the  case  of  a  ruptured  steam 
pipe  the  valves  controlling  the  flow  of  steam  to  the  point  of 
rupture   each   way   should   be    closed   at   the   earliest   possible 
moment,  as  the  escape  of  steam  will  soon  make  it  impossible  to 
remain  in  the  fire-room  with  safety.     If  it  is  arranged  to  work 
the  stop-valves  from  the  deck  above,  this  is  readily  effected, 
and  the  trouble  thus  gotten  under  control.     Self-closing  valves 
are  also  often  provided  in  modern  practice,  as  referred  to  in 
Section  17  [3].    It  is  not  possible,  however,  to  so  fit  these  that 
they  will  always  act,  or  that  they  will  shut  off  the  steam  in  more 
than  one  direction.     In  one  way  or  another,  however,  the  first 
attempt  must  be  to  shut  off  the  escape  of  steam.     The  next 
thought  must  be  for  the  boilers,  to  safeguard  those  which  may 
have  been  shut  off  from  the  engine  from  danger  due  to  increase 
of  pressure,  and  those  which  still  remain  connected  to  the  engine 
from  danger  due  to  low  water.     The  particular  steps  suitable 
for  attaining  these  objects  have  been  already  sufficiently  dis- 
cussed, and  no  further  mention  will  be  here  necessary. 

(10)  Casualties  With  Water -Tube  Boilers. — With  water-tube 
boilers  the  same  general  emergencies  are  liable  to  arise  as  with 
fire-tube  boilers,  and  may  be  met  in  the  same  general  way.     It 
should  be  remembered,  however,  that,  due  to  the  small  amount 
of  water  carried,  the  results  due  to  shortness  of  water  will  come 
much  more  rapidly  than  with  fire-tube  boilers,  and  promptness 
in  action  is  all  the  more  necessary.     In  such  boilers  the  tubes 
are  most  liable  to  suffer  through  shortness  of  water,  and  any 
considerable;  overheating  is   likely  to   result   in   their   rupture. 
With  the  small  tube  type  the  most  serious  results  of  such  an 


298  PRACTICAL  MARINE  ENGINEERING. 

accident  are  usually  confined  to  the  emptying  of  the  contents  of 
the  boiler  into  the  fire,  and  the  effectual  deadening  or  extinction 
of  the  latter.  Here,  as  before,  however,  with  more  than  one 
boiler  the  trouble  must  be  localized  by  shutting  off  the  boiler 
with  the  ruptured  tubes  from  connection  with  the  others.  In 
other  cases,  however,  with  large  tube  types  especially,  or  with 
the  rupture  of  steam  or  water  drums,  the  consequences  may  be 
more  serious,  resulting  in  driving  every  one  from  the  fire-room, 
or  even  in  loss  of  life.  The  same  general  principles  apply  here, 
however,  as  with  fire-tube  boilers,  and  good  judgment  must  be 
depended  on  for  the  details  suitable  to  the  occasion. 

Sec.  39.    ENGINE-ROOM  ROUTINE  AND  MANAGEMENT, 
[i]  Getting  Under  Way. 

In  the  engine  room  the  same  as  in  the  fire-room,  a  general 
inspection  is  first  in  order,  more  or  less  detailed  and  extensive, 
according  to  the  time  the  machinery  has  been  out  of  use,  and 
the  degree  of  acquaintance  with  its  various  features  and  pecu- 
liarities. If  the  engine  has  been  laid  up  for  any  length  of  time 
a  detailed  examination  will  of  course  be  required  similar  to  that 
referred  to  at  a  later  point  in  Sec.  43.  We  here  assume,  how- 
ever, that  no  such  general  overhauling  is  needed,  and  that  the 
machinery  is  to  be  supposed  in  a  working  condition. 

A  good  general  idea  should  first  be  obtained  of  the  lead 
of  the  principal  piping  systems  as  noted  in  Sec.  25,  and  especially 
of  the  main  and  auxiliary  steam  and  feed  systems.  These  lines 
of  piping  should  be  looked  over,  the  location  of  the  valves 
noted,  and  where  permissible  the  valves  should  be  opened  or 
closed  to  insure  their  being  in  working  order,  and  then  left  in 
the  condition  desired  for  getting  up  steam. 

The  various  parts  of  the  main  engine  will  be  looked  over 
so  as  to  insure,  so  far  as  an  external  examination  can,  that 
everything  is  in  proper  working  order. 

The  various  auxiliaries  will  be  looked  over  in  the  same 
way,  and  the  results  of  this  general  examination  being  satis- 
factory, steps  may  be  taken  to  test  the  various  parts  of  the  ma- 
chinery under  steam  as  soon  as  dt  is  ready. 

We  have  already  in  Sec.  38  pointed  out  the  importance  of 
trying  the  feed-pumps  and  getting  them  into  working  order  as 
soon  as  possible,  in  order  to  insure  the  proper  supply  of  feed- 
water  to  the  boiler.  Next  in  order  may  come  the  circulating 


OPERATION,  MANAGEMENT  AND  REPAIR.  299 

pump,  the  engine  of  which  is  started  at  moderate  speed,  and  the 
main  injection  and  discharge  valves  opened.  In  starting  all  of 
this  auxiliary  machinery,  proper  precautions  must,  of  course, 
be  observed  in  regard  to  freeing  the  steam  cylinders  of  con- 
densed water  by  means  of  the  relief  valves, as  noted  in  Sec.  38  [3] 
in  connection  with  the  feed-pump.  The  circulating  pump  being 
usually  below  the  level  of  the  water  outside  the  ship,  it  naturally 
floods  itself  so  that  no  trouble  should  be  met  with  in  getting  it 
to  take  water.  Assuming  the  air-pump  independent,  this  may 
be  started  next  and  put  at  a  moderate  pace,  or  sufficient  to  main- 
tain a  vacuum  of  15  to  20  inches. 

The  electric  light  engines,  if  not  in  operation  from  the 
donkey  boiler,  will  also  be  looked  after  and  started  in  due  time, 
as  well  as  any  other  auxiliary  machinery  whose  operation  may 
be  required  for  getting  under  way. 

In  case  the  main  engine  since  the  last  time  used  has  been 
subjected  to  any  adjustment  or  overhauling,  it  will  be  well  to 
turn  it  completely  over  with  the  turning  engine  once  or  twice 
in  order  to  make  sure  that  everything  is  clear  and  in  running 
condition. 

In  the  meantime,  while  the  auxiliaries  are  being  gotten  into 
operation,  the  steam  will  have  been  admitted  to  the  jackets,  if 
there  are  any,  and  to  the  cylinders  through  the  main  stop  and 
throttle  valves.  Here,  as  noted  in  Sec.  38  [i],  the  object  in  view 
is  to  avoid  any  sudden  change  in  the  temperature  or  heat  condi- 
tion of  the  machinery.  A  good  method  of  gradually  warming1 
up  the  engine  is  to  just  unseat  the  main  stop  and  throttle  valves, 
and  then  with  the  links  in  the  ahead  gear,  say,  to  slowly  turn 
the  engine  over  ahead  with  the  turning  engine.  This  will  allow 
the  steam  to  work  its  way  through  the  engine,  warming  up  the 
entire  series  of  cylinders  and  bringing  them  practically  to  their 
working  temperatures.  The  water  condensed  must,  of  course, 
be  allowed  to  escape  by  opening  the  relief  and  drain  valves. 
During  this  period  the  reversing  gear  will  also  be  warmed  up 
and  tried  under  steam  until  it  works  properly  and  throws  the 
links  smoothly  from  one  side  to  the  other. 

When  the  engine  has  thus  become  well  warmed  up,  the 
turning  gear  will  be  disconnected  and  locked  out  of  gear,  and  im- 
mediate preparations  made  for  turning  over  under  steam.  At 
this  point  the  question  of  lubrication  must  be  borne  in  mind,  and 
while  the  regular  schedule  of  oiling,  etc.,  need  not  be  started 


300  PRACTICAL  MARINE  ENGINEERING. 

until  the  ship  is  fairly  under  way,  still  a  moderate  provision  of 
oil  may  be  made  to  the  more  important  bearings,  and  if  the  en- 
gine has  been  out  of  use  some  little  time,  it  will  be  well  to  work 
oil  into  the  principal  bearings  during  the  preceding  operation 
of  the  main  engine  with  the  turning  gear  as  suggested  above. 

Before  turning  over  under  steam  the  deck  officer  should 
be  notified  in  order  that  the  hawsers  securing  the  ship  to  the 
dock  may  be  looked  to  if  necessary,  or  the  presence  of  anything 
about  the  stern  which  might  foul  or  jam  the  propeller  may  be  re- 
ported back  to  the  engine  room.  Everything  being  in  readiness, 
the  main  stop  valve  is  opened  slowly  to  full  opening,  and  steam 
is  turned  on  the  reversing  gear.  Then  the  main  throttle  being 
still  closed  the  links  are  thrown  back  and  forth  a  few  times,  the 
passover  or  starting  valves  opened,  and  the  throttle  opened 
moderately.  If  the  engine  does  not  start  off  in  one  direction 
the  links  are  thrown  into  the  other  gear,  and  if  everything  is  in 
the  proper  condition  the  engine  will  start  in  one  direction  or  the 
other  after  a  few  see-saws  of  the  links.  The  hand  relief  valves 
are,  of  course,  operated  at  the  same  time  in  order  to  aid  in 
freeing  the  cylinders  of  any  water  which  may  collect  there,  or 
which  may  enter  with  the  steam.  Often  the  engine  will  move 
a  little  way,  but  the  high  pressure,  or  one  of  the  other  pistons 
will  not  pass  the  center.  This  is  on  account  of  the  water  in  the 
cylinders,  and  is  especially  liable  to  occur  if  the  engine  has  not 
been  well  warmed  up,  or  if  the  steam  pipe  has  not  been  properly 
drained.  In  such  case  the  water  must  be  worked  out  through 
the  relief  and  drain  valves,  the  links  in  the  meantime  being 
moved  back  and  forth.  In  answer  to  this  the  piston  will  see- 
saw up  and  down,  getting  gradually  nearer  the  center,  and 
finally  when  the  water  is  sufficiently  cleared  out,  passing  over 
and  continuing  the  revolution.  As  the  main  engine  is  thus 
started  the  circulating  pump  and  air  pump,  if  independent,  will  be 
started  up  at  the  increased  pace  suitable  to  the  amount  of  steam 
passing  through  the  engine  and  into  the  condenser.  After  thus 
running  for  a  few  minutes,  or  until  everything  seems  to  be  in 
proper  running  order,  the  engine  is  stopped,  and  the  signal  for 
the  regular  start  is  awaited.  The  object  of  thus  turning  over 
under  steam  is  simply  to  make  sure  that  everything  is  free  and  in 
working  condition.  Little  of  course,  can  be  told  regarding  the 
adjustment  of  the  various  bearings,  etc.,  or  their  liability  to  heat 
or  pound.  If  the  machinery  is  new  or  has  undergone  any  con- 


OPERATION,  MANAGEMENT  AND  REPAIR.  301 

siderable  readjustment,  or  has  been  out  of  use  a  long  time,  it 
should  have  a  dock  trial  of  some  considerable  time,  in  order  to 
determine  the  various  points,  and  to  bring  out  any  defects  liable 
to  present  themselves  in  the  course  of  a  continuous  run. 

Naturally  the  time  when  the  ship  is  to  start  will  be  known 
to  the  engineer,  and  these  various  preparations  will  be  so  timed 
that  soon  after  the  final  turning  over  under  steam,  the  signal  for 
the  regular  start  may  be  expected. 

PASSAGE  OF  STEAM  THROUGH   THE  ENGINE. 

In  connection  with  the  operation  of  a  marine  engine  it  will 
be  instructive  to  note  in  order  the  names  of  the  various  parts 
through  which  the  steam  passes  from  the  boiler  until  it  returns 
again  as  feed  water  to  its  starting  point.  Starting,  then,  with 
its  formation  in  the  boiler,  we  have  the  following  route  for  the 
case  of  an  ordinary  triple-expansion  engine : 

Dry-pipe — Safety  valve  chamber — Boiler  stop-valve — 
Boiler  steam-pipe — Main  steam-pipe — Main  stop-valve — Main 
throttle-valve — High  pressure  valve-chest — Steam  ports  and 
passages — High  pressure  cylinders — Steam  passages  and  ports 
—Exhaust  side  of  valve — Exhaust  passage — Exhaust  pipe  to  in- 
termediate valve-chest  and  cylinder  as  above  for  the  high  pres- 
sure— Exhaust  pipe  to  low  pressure  valve-chest  and  cylinder 
as  above  for  the  high  pressure — Exhaust  pipe  to  condenser — 
Condenser — Air-pump  suction — Foot-valves — Air-pump  cham- 
ber— Bucket-valves  — Delivery-valves  —  Hot-well — Feed  pump 
suction  —  Induction  valves  —  Feed-pump  barrel  —  Discharge 
valves — Feed-pipe — Check-valve — Boiler. 

In  addition  a  separator  may  appear  between  the  boiler  and 
the  engine,  and  the  filter  and  feed  water  heater  between  the  hot- 
well  and  the  boiler. 

[a]  Routine  Operation. 

In  the  routine  operation  of  the  main  engine  and  of  the 
other  machinery  in  the  engine  room,  the  following  are  the  points 
requiring  chief  consideration : 

(a)  The  proper  provision  of  oil  and  other  lubricant  in  suit- 
able quantities  and  at  proper  intervals,  or  continuously,  accord- 
ing to  the  nature  of  the  oiling  gear  in  use. 

(b)  A    constant    watch    over   the    general    conditions    of 
operation    of   the    machinery   in   order   that    any    symptom    or 


302  PRACTICAL  MARINE  ENGINEERING. 

sign   of  derangement   or   disturbance   may  be   noted,   and   the 
proper  steps  taken  for  its  control  or  removal. 

The  chief  points  relating  to  lubrication  have  been  already 
discussed  in  Sec.  24  [12].  The  watch  over  the  general  condi- 
tions extends  to  all  features  and  depends  to  such  an  extent  upon 
the  special  circumstances  that  only  a  few  general  hints  can  be 
given. 

First,  regarding  the  sounds  which  accompany  the  opera- 
tion of  the  machinery  and  the  part  the  ear  may  take  in  de- 
tecting symptoms  of  disturbance.  The  operation  of  the  main 
engine  and  of  the  various  parts  of  the  machinery  individually  is 
accompanied  by  more  or  less  plainly  marked  sounds  or  noise  or 
combination  of  sounds.  These  in  the  end  tend  to  combine  them- 
selves into  a  kind  of  resultant  rumble,  click,  and  rattle,  which 
often  remains  quite  constant  in  character,  and  so  comes  to  have 
a  kind  of  individuality  of  its  own.  To  a  person  accustomed  to 
the  regular  sounds  of  the  engine  room,  the  ear  is  often  a  deli- 
cate means  of  detecting  any  departure  from  the  regular  routine, 
and  often  the  first  indication  of  some  disturbance  will  be  fur- 
nished by  a  change  in  the  character  of  the  sounds  produced. 
In  particular,  any  unusual  pound,  jar,  squeak  or  rattle  should  be 
located  as  soon  as  possible,  and  its  cause  investigated. 

In  some  cases  assistance  in  the  detection  or  location  of  a 
pound  or  knock  may  be  gained  by  the  use  of  a  convenient  piece 
of  metal,  such  as  a  spanner,  or  bit  of  pipe,  one  end  being  placed 
to  the  ear  and  the  other  against  the  cylinder,  valve-chest,  or 
other  point  nearest  to  where  trouble  is  expected.  At  the  same 
time  too  much  reliance  must  not  be  placed  on  the  ear  to  the 
neglect  of  other  means  of  observation.  In  fact  in  the  modern 
engine  room  all  of  the  available  senses  keenly  on  the  alert  will 
be  found  none  too  many  for  the  proper  watch  and  care  over 
the  machinery  in  use. 

The  danger  of  heating,  due  to  insufficient  lubrication,  poor 
adjustment  or  bad  condition  of  bearing,  is  one  which  the  ear 
will  often  aid  in  detecting,  but  the  chief  reliance  must  be  placed 
on  the  sense  of  feeling  and  on  the  nose.  With  the  necessary 
skill  most  of  the  important  bearings  may  be  felt  by  the  hand. 
Caution  must  be  used,  however,  so  that  the  hand  may  not  be 
caught  or  jammed.  This  part  of  an  engineer's  training  is  one 
which  can  be  learned  only  by  observation  and  cautious  trial.  If 
the  heating  of  the  bearing  passes  beyond  a  moderate  elevation 


OPERATION,  MANAGEMENT  AND  REPAIR.  303 

of  temperature,  the  oil  will  become  correspondingly  heated  and 
will  give  off  a  burnt  odor,  or  perhaps  will  smoke  freely,  thus  show- 
ing plainly  the  existence  of  trouble.  The  nose  and  eye  will  thus 
come  in  as  factors  in  detecting  trouble  of  this  character. 

Small  steam  leaks  at  joints,  stuffing-boxes,  etc.,  will  make 
themselves  plainly  visible,  and  should  receive  such  treatment  as 
the  circumstances  may  require,  in  order  that  they  may  be 
closed  up.  It  must  not  be  forgotten  that  every  steam  leak 
means  a  loss  of  both  heat  and  fresh  water. 

The  vacuum  in  the  condenser  will  depend  not  only  on  the 
proper  operation  of  the  air-pump,  but  also  on  the  reduction  of 
all  possible  air  leaks  which  might  admit  air  to  the  low  pressure 
cylinder  during  the  exhaust,  or  to  the  steam  side  of  the  conden- 
ser. All  such  stuffing-boxes,  joints,  etc.,  must  therefore  receive 
careful  attention,  especially  if  the  vacuum  is  not  what  it 
should  be. 

Water  coming  over  into  the  cylinders  from  the  boilers  pro- 
duces a  crackling  or  snapping  noise,  which  is  readily  recog- 
nized. The  automatic  relief  valves  may,  of  course,  be  depended 
on,  or  the  hand  gear  may  be  operated  to  aid  in  removing  the 
disturbing  cause. 

In  stopping  momentarily  the  throttle  is  closed  and  the  links 
are  run  to  mid-gear,  no  other  change  being  made,  and  every- 
thing remaining  ready  to  start  again  at  an  instant's  notice.  In 
stopping  for  a  known  period  of  time  of  any  considerable  dura- 
tion, means  should  be  taken  to  stop  the  flow  of  oil  to  the  bear- 
ings by  the  closure  of  the  feeding  valves  or  the  withdrawal  of 
wicks,  according  to  the  means  in  use.  If  the  stop  is  only  tem- 
porary, and  the  engines  are  to  be  kept  in  readiness  for  starting 
again,  the  further  steps  taken  will  be  only  such  as  will  serve 
to  bring  the  machinery  into  its  condition  just  previous  to  getting 
under  way.  That  is,  the  circulating  and  air-pumps,  so  far  as  in- 
dependent, may  be  slowed  somewhat,  while  by  the  aid  of  the 
steam  jackets,  if  fitted,  and  steam  which  is  allowed  to  flow  past 
the  stop  and  throttle  valves,  the  main  engine  is  kept  warmed  up 
and  ready  for  operation  at  short  notice. 

If  the  stop  is  to  be  of  longer  duration  and  the  steam  is  to 
be  shut  off  the  engine,  the  stop  and  throttle  valves  will  be 
closed,  the  air  and  circulating  pumps  shut  down,  and  steam 
shut  off  the  reversing  engine,  jackets,  etc.  The  various  drain 
valves  and  drips  will  be  left  open  so  as  to  free  the  machinery, 


304  PRACTICAL  MARINE  ENGINEERING. 

as  far  as  possible,  of  all  the  water  formed  by  the  gradual  con- 
densation of  the  steam.  At  the  same  time  the  flow  of  oil  to  the 
bearings  will  be  shut  off  and  such  measures  taken  with  respect 
to  the  oiling  gear  as  the  circumstances  may  require. 

[3]  Minor  Emergencies  and  Troubles. 

We  will  now  consider  briefly  the  steps  to  be  taken  in  the 
event  of  the  more  commonly  occurring  troubles,  some  of  which 
have  been  mentioned  in  the  preceding  paragraph. 

(i)  Derangement  in  the  Oiling  Gear. — In  sight-feed  apparatus 
this  is  readily  detected,  and  without  loss  of  time  the  trouble 
must  be  located  and  remedied,  the  oil  in  the  meantime 
being  supplied  to  the  bearing  in  question  by  hand.  The  trouble 
in  such  cases  usually  arises  from  a  clogging  up  of  some  of  the 
pipes  or  passages,  and  as  noted  in  Sec.  24  [12]  all  such  pipes 
should  be  put  up  with  union  joints  so  that  they  may  be  readily 
taken  down,  cleaned  and  replaced. 

(2)  Hot  Bearing. — This  is  one  of  the  most  important  of  the 
minor  troubles  which  may  arise  in  the  engine  room,  and  one 
which  may  lead  to  serious  consequences  in  case  the  proper  steps 
for  its  control  are  not  taken  in  time.  A  hot  bearing  may  arise 
from  a  variety  of  causes,  among  which  the  following  are  the 
more  important. 

(a)  Lack  of  lubrication. 

(b)  Lubricant  too  thin  so  that  it  will  not  remain  in  place  in 
the  bearing  and  sustain  the  load. 

(c)  Improper  adjustment,  the  amount  of  clearance  between 
journal  and  brass  being  too  small. 

(d)  Lack  of  alignment  in  the  machinery,   as  a   result  of 
which  the  bearing  is  excessively  severe  on  certain  parts,  thus 
forcing  out  the  lubricant  and  causing  the  surface  to  nip  and 
abrade. 

(e)  Bearing  surface  not  of  sufficient  area  to  carry  the  load 
or  take  the  work  put  upon  it  without  an  undue  rise  in  tem- 
perature.   This  means,  of  course,  either  that  the  design  is  faulty 
or  that  the  machinery  is  worked  beyond  the  loads  for  which  it 
was  intended. 

(f)  Bearing  surfaces  rough  and  uneven,  due  to  the  poor 
workmanship,  or  as  a  result  of  serious  heating  on  a  previous 
occasion. 

If  the  trouble  is  due  to  a  lack  of  lubrication  simply,  and 


OPERATION,  MANAGEMENT  AND  REPAIR.  305 

is  discovered  in  time,  an  abundant  supply  of  oil  will  be  usually 
sufficient  to  control  the  condition  and  to  gradually  bring  the 
bearing  back  to  its  normal  temperature.  If,  however,  the  tem- 
perature rises  considerably,  the  journal  may  expand  more  than 
the  bearing  brasses,  so  that  the  clearance  will  be  decreased  and 
the  brasses  will  pinch  the  journal,  thus  introducing  a  further 
source  of  trouble  as  noted  in  (c)  above.  If  this  is  not  soon 
relieved,  the  metal  surfaces  will  nip  and  the  softer  of  the  two 
will  begin  to  abrade  or  "cut."  This  is  always  the  bearing 
metal,  and  the  resulting  condition,  in  consequence  of  which  the 
smoothness  of  the  surface  is  destroyed,  will  tend  simply  to  make 
matters  still  worse,  to  generate  more  heat,  expand  the  parts 
still  more,  perhaps  nip  the  surfaces  still  more  tightly,  and  so  cut 
the  worse,  until  the  bearing  metal  melts  and  runs  out. 

The  treatment  of  a  heated  bearing  involves  two  chief  items, 
viz.,  the  removal  of  the  cause  and  the  restoration  of  the  bearing 
to  its  normal  condition. 

We  may  remove  the  cause  entirely,  of  course,  by  stopping 
the  engine,  and  in  an  advanced  case  of  trouble,  such  as  just 
described,  this  may  be  necessary.  Otherwise  we  may  reduce  the 
cause  by  slowing  down  somewhat,  and  thus  decreasing  the 
amount  of  work  thrown  on  the  bearing.  We  may  further  de- 
crease the  cause  by  easing  up  the  bearing  cap  and  thus  increas- 
ing the  clearance  between  journal  and  bearing  surface.  This, 
however,  can  only  be  done  to  a  slight  extent,  else  trouble  will 
be  met  with  from  too  great  clearance  and  the  consequent  pound- 
ing in  the  joint. 

A  plentiful  supply  of  oil,  or  other  lubricant,  will  also  aid  in 
decreasing  the  cause  and  in  restoring  matters  to  their  proper 
condition. 

A  decrease  in  temperature  will  also  usually  aid  in  removing 
the  cause,  and  is,  furthermore,  of  course,  one  of  the  chief  steps 
in  bringing  the  bearing  back  to  its  normal  condition. 

To  this  end  in  the  extreme  case,  it  may  be  considered  neces- 
sary to  turn  a  stream  of  water  on  the  bearing,  thus  to  absorb 
and  carry  away  the  heat,  and  in  many  cases  full  power  trials  are 
run  with  streams  of  water  playing  for  a  considerable  part  of  the 
time  on  various  parts  of  the  machinery  in  order  to  carry  off  the 
heat  and  so  control  the  temperature.  Water,  however,  is  doubt- 
less used  far  more  than  is  absolutely  necessary,  and  far  more 
than  good  engineering  would  authorize.  If  sprayed  or  run  from 


3o6  PRACTICAL  MARINE  ENGINEERING. 

a  hose  on  the  bearings  it  is  almost  certain  to  find  its  way  in  and 
an  to  the  bearing  surfaces,  where  it  will  prevent  action  of  the 
lubricant.  For  this  reason  its  use  once  begun,  it  may  be  neces- 
sary to  continue,  simply  because  the  lubricant  cannot  lubricate 
in  the  presence  of  water.  In  the  best  modern  practice,  as  indi- 
cated in  Sec.  21  [n],  provision  is  made  for  circulating  water 
through  hollow  bearing  blocks,  and  thus  in  the  most  effective 
way  the  water  is  able  to  remove  the  heat  generated  without 
coming  into  contact  with  the  bearing  surface  itself. 

In  case  the  machinery  is  not  properly  lined  up,  or  the  bear- 
ings are  of  insufficient  area,  or  not  in  proper  condition,  only 
temporary  relief  can  be  looked  for  from  the  various  means  sug- 
gested above,  the  most  effective  of  which  will  presumably  be  the 
operation  of  the  machinery  at  a  low  or  moderate  power  until 
such  time  as  the  needed  readjustments,  changes  or  repairs  can 
be  effected. 

To  sum  up  the  treatment  for  a  hot  bearing,  the  measures 
taken  may  be  selected  according  to  judgment  and  the  special 
circumstances  from  the  following: 

Lubrication. 

Easing  up  bearing  caps. 

Slowing  down  and  consequent  reduction  of  load. 

Application  of  water. 

(3)  Pounding. — This  condition  may  arise  from  several 
causes,  chief  among  which  are  the  following : 

(a)  Bearings  not  in  proper  adjustment,  too  much  clearance 
being  allowed  between  journal  and  bearing  metal.     (See  Sec. 
24  [12].) 

(b)  Lubricant  too  thin  and  thus  unable  to  retain  its  place 
in  the  bearing. 

(c)  Valve  events  not  properly  adjusted,  especially  the  ex- 
haust closure  and  following  compression. 

Furthermore,  an  engine  will  often  show  at  different  speeds 
a  marked  difference  in  this  respect,  such  difference  being  chiefly 
due  to  the  increasing  effect  of  the  inertia  forces  with  increase  in 
the  revolutions. 

If  the  trouble  arises  from  the  nature  of  the  lubricant  in 
use  a  change  to  a  heavier  oil  may  show  an  improvement.  If, 
however,  as  is  more  commonly  the  case,  it  is  due  to  faulty  ad- 
justment, either  of  bearing  or  valve  gear,  or  both,  but  little  can 
be  done  while  the  engine  is  in  operation,  and  the  first  oppor- 


OPERATION,  MANAGEMENT  AND  REPAIR.  307 

tunity  for  overhauling  and  readjustment  must  be  taken  for  a 
study  of  the  conditions,  both  as  regards  the  bearings  them- 
selves, and  the  possibility  of  improvement  by  an  adjustment  of 
the  compression.  If  the  pounding  becomes  very  severe,"  it  may 
become  necessary  to  slow  down  the  engine  and  operate  under 
less  than  the  regular  or  full  power  until  the  proper  examination 
and  readjustment  can  be  made. 

(4)  Priming  or  Lifting  Water. — This  emergency  has  been 
more  particularly  referred  to  in  Sec.  38  [3] .    In  small  quantities 
water  produces  a  crackling  or  snapping  sound  in  the  cylinders, 
and  the  automatic  relief  valves  may  be  allowed  to  take  care  of 
the  situation,  of  if  desired,  the  hand  reliefs  may  be  operated  as 
well.     If,  however,  the  water  comes  over  in  large  quantities  the 
engine  will  slow  down  and  work  with  an  irregular  and  labored 
motion,  which  may  be  readily  recognized  as  denoting  this  con- 
dition.   In  such  case  the  throttle  or  main  stop  valve  should  be 
partially  closed  and  the  water  gotten  rid  of  as  quickly  as  possible 
by  the  use  of  the  relief  valves.  The  engine  will  then  operate  at  the 
reduced   speed   permitted   by  the   partially   closed   valve,   pre- 
sumably without  further  trouble.     If  on  opening  out  again  the 
tendency  to  lift  water  at  full  or  ordinary  power  is  persistent,  the 
power  must  be  reduced  until  the  trouble  is  removed  and  the 
engine   will   operate   continuously  without   disturbance   of  this 
character. 

(5)  Vacuum  Falls  and  Becomes  Poor  While  the  Condenser  Be- 
comes Hot. — Following  are  the  chief  causes  which  may  lead  to 
such  a  condition : 

(a)  Insufficient  condensing  water  from  any  cause. 

(b)  Division  plate  in  condenser  head  carried  away  so  that 
water  goes  directly  from  inflow  to  outflow  without  going  through 
the  tubes. 

(c)  Excessive  inflow  of  steam  caused  by  leakage  either  past 
low  pressure  piston  or  slide  valve,  or  possibly  in  the  ''bleeder" 
of  "silent  blow"  if  such  is  fitted. 

(6)  Vacuum  Falls  and  the  Condenser  Remains  Cool. — In  such 
case  the  indications  are  that  this  condition  is  due  to  the  presence 
of  air  not  removed  by  the  air  pump,  as  may  be  caused  by  any 
one  or  a  combination  of  any  of  the  following : 

(a)  Air-pump  valves  defective. 

(b)  Leak  in  the  condenser,   either  at  the  head  joints  or 
through  a  crack. 


3o8  PRACTICAL  MARINE  ENGINEERING. 

(c)  Soda  or  drain  cocks  open  or  leaking. 

(d)  Low  pressure  piston  rod  stuffing  box  leaking  air  inward 
during  exhaust  stroke. 

(e)  With  "inside"  piston  valves  on  the  low  pressure  cylin- 
der, leaky  valve  stem  stuffing  boxes. 

(f)  Leak  or  obstruction  in  the  pipe  leading  to  the  vacuum 
gauge. 

Sec.  40.    BOH,ER  CORROSION. 

NO  sooner  has  a  boiler  been  completed  than  the  various 
corrosive  and  destroying  influences  with  which  it  is  surrounded 
set  to  work  on  its  destruction.  We  may  conveniently  consider 
corrosion  as  of  two  kinds,  that  due  to  oxygen  and  that  due  to 
an  acid.  These  two  are,  however,  by  no  means  independent, 
and  are  often  combined  in  very  complex  ways.  The  process  by 
which  oxygen  combines  with  another  substance  is  called  oxida- 
tion, and  the  product  of  the  operation  an  oxide.  In  the  case  of 
iron  and  steel  the  typical  product  is  the  ordinary  red  iron  rust, 
or  ferric  oxide  (Fe2  O8),  consisting  of  about  56  parts -by  weight 
of  iron  and  24  of  oxygen.  In  order  that  oxidation  or  rusting  of 
iron  may  continuously  proceed  at  ordinary  temperatures,  how- 
ever, it  is  not  enough  that  oxygen  and  iron  shall  be  in  contact. 
It  requires  the  additional  presence  of  moisture  and  carbon  di- 
oxide (CO2),  small  proportions  of  which  are  always  present  in 
the  atmosphere.  Oxygen  and  moisture  alone  act  feebly  and 
very  slowly  on  iron,  but  when  the  four  substances,  iron,  oxygen, 
moisture,  and  carbon  dioxide,  are  all  present  together,  the 
operation  of  rusting  proceeds  continuously  and  with  vigor. 
Oxide  is  first  formed,  and  this  is  reduced  by  the  carbon  dioxide 
to  a  carbonate,  and  this  in  turn  breaks  up,  forming  hydrated 
oxide  (FeHO2),  setting  free  the  carbon  dioxide  to  continue  the 
process.  The  hydrated  oxide  thus  formed  is  furthermore  elec- 
tro-chemically  negative  to  iron,  and  thus  helps  on  the  operation 
as  explained  at  a  later  point.  If  either  the  moisture  or  the  car- 
bon dioxide  is  absent  the  oxygen  will  have  little  or  no  effect, 
and  the  iron  will  be  protected.  This  is  shown  by  the  non-rust- 
ing of  iron  in  perfectly  dry  air,  even  though  there  may  be  some 
carbon  dioxide  present ;  or  again,  by  its  preservation  in  a  weak 
alkaline  liquid,  as  lime  water,  in  which  there  can  be  no  free  car- 
bon dioxide.  The  piano  wire  used  in  certain  forms  of  deep  sea 
sounding  apparatus,  for  example,  is  thus  kept  from  corrosion 


OPERATION,  MANAGEMENT  AND  REPAIR.  309 

under  conditions  which  would  naturally  soon  destroy  its  regu- 
larity and  value  for  the  purpose  used. 

Acid  corrosion  means  the  attacking  of  a  substance  by  an 
acid,  the  breaking  up  of  the  latter,  and  the  formation  of  a  new 
substance  known  as  a  salt,  and  composed  of  a  part  of  the  acid 
and  of  the  substance  attacked.  Thus  hydrochloric  or  muriatic 
acid  (HC1),  as  it  is  commonly  called,  is  sometimes  present  in 
boilers.  This  is  composed  of  hydrogen  and  chlorine.  When  it  is 
brought  into  the  presence  of  iron  or  steel  the  chlorine  leaves  the 
acid,  and  joining  with  the  iron,  forms  a  salt  known  as  ferrous 
chloride,  or  chloride  of  iron  (FeCl2).  With  iron  rust  and  mu- 
riatic acid  the  result  would  be  similar,  the  chlorine  would  join 
with  the  iron  and  form  ferrous  chloride,  while  the  hydrogen  of 
the  acid  would  join  with  the  oxygen  of  the  oxide  and  form 
water. 

As  before  stated,  acid  corrosion  and  oxidation  are  very 
commonly  both  present,  especially  in  the  latter  operation,  and 
in  fact  the  continued  progress  of  oxidation  with  iron,  moisture 
and  carbon  dioxide  is  dependent  on  the  combined  action  of  both 
operations.  WTe  shall  not,  however,  deal  further  with  the 
chemical  details  of  corrosion  in  general,  but  proceed  to  a  brief 
consideration  of  the  causes,  effects  and  remedies  as  related  to 
corrosion  in  marine  boilers. 

Taking  first  the  exterior  o'f  boilers  and  of  all  exposed  iron 
and  steel  work  in  general,  it  is  clear  that  the  conditions  for  con- 
tinued rusting  are  all  present  on  board  ship.  The  air  is  moist 
and  there  is  likely  to  be  present  carbon  dioxide  in  abundance. 
The  only  safe  protection  is,  therefore,  a  covering  which  shall 
keep  the  air,  moisture  and  carbon  dioxide  from  contact  with  the 
iron.  To  this  end  metal  paint  or  other  equivalent  coating  is 
used  wherever  possible.  Many  small  fittings,  especially  about 
the  deck,  are  of  galvanized  iron,  that  is,  iron  covered  with  a  thin 
coating  of  zinc.  The  latter  metal  is  but  slightly  affected  by  the 
process  of  oxidation,  and  it,  therefore,  forms  an  efficient  protec- 
tion for  the  iron.  Brass,  bronze  and  copper  are  also  oxidized 
but  slightly,  and  the  oxide  formed  serves  as  a  protective  cover- 
ing to  the  metal  underneath.  For  this  reason,  among  others, 
many  of  the  fittings  about  boilers  and  elsewhere  are,  as  we  have 
already  seen,  made  of  these  metals. 

Passing  in  now  to  the  fire  side  of  the  boiler,  we  find  the  ap- 
plication of  paint  or  other  protective  coating  impracticable. 


3io  PRACTICAL  MARINE  ENGINEERING. 

Here  we  must  depend  on  the  heat,  which  will  so  dry  the  air  that 
it  is  no  longer  moist.  That  is,  while  water  vapor  may  still  be 
present  in  the  air,  there  is  so  little  compared  with  the  amount 
the  air  could  naturally  contain  at  that  temperature,  that  it  is 
held  by  the  air  and  is  no  longer  free  to  enter  as  a  factor  into 
the  operation  of  oxidation.  Rusting  in  the  usual  way  is,  there- 
fore, very  much  retarded  or  prevented.  To  this  fact  we  owe  the 
general  preservation  of  the  furnaces,  ash-pits,  etc.,  from  serious 
and  continued  corrosion.  We  here,  however,  run -into  another 
danger  in  the  extreme  case  when  oxygen  is  present  in  excess, 
and  both  the  oxygen  and  iron  are  very  hot.  The  oxygen  in 
such  cases  enters  more  readily  into  union  with  the  iron,  and  if 
the  temperatures  should  be  sufficient,  a  different  kind  of  oxide 
is  formed,  the  black,  or  magnetic  oxide  (Fc8O4),  the  same  as  the 
mill  scale  or  forge  scale,  which  forms  when  iron  is  worked  at  a 
red  heat.  The  oxide  thus  formed  may  presumably  be  swept 
away  by  the  scouring  action  of  the  draft,  thus  exposing  a  fresh 
surface  to  renewed  attack.  The  back  ends  of  the  tubes  seem 
especially  liable  to  attack  in  this  way,  and  particularly  with  hard 
forced  draft.  The  cure  for  this  trouble  is  found  in  the  use  of  cast 
iron  ferrules,  as  previously  described. 

These  ferrules  protect  the  tube  ends  from  the  extremes  of 
temperature,  and  also  provide  something  for  the  hot  oxygen 
to  attack,  while  they  are  readily  renewed. 

Turning  now  to  the  water  side  of  the  boiler,  we  find  more 
serious  trouble  than  with  the  fire  side.  There  is  likely  to  be 
more  or  less  air  in  the  feed  water,  either  entering  with  the 
make-up  feed,  or  occasionally  drawn  into  the  feed-pump  and 
sent  on  to  the  boiler.  There  may  also  be  free  carbon  dioxide 
liberated  from  the  salts  entering  with  the  make  up  feed,  and 
thus  all  the  conditions  for  continuous  rusting  may  be  present. 
Even  if  free  carbon  dioxide  is  not  present  the  formation  of  iron 
oxide,  combined  with  electro-chemical  reactions,  as  referred  to 
later,  may  result  in  serious  local  corrosion.  Furthermore,  as 
the  feed-water  is  heated  the  air  is  liberated,  and  the  oxygen  just 
at  the  instant  of  liberation  seems  to  be  especially  active  chemi- 
cally, and  is  thus  all  the  more  likely  to  attack  exposed  places 
than  if  allowed  to  remain  in  solution  in  the  water,  as  at  ordin- 
ary temperatures. 

Turning  next  to  acid  corrosion,  mention  may  first  be  made 
of  the  serious  trouble  formerly  experienced  from  the  use  of 


OPERATION,  MANAGEMENT  AND  REPAIR.  311 

animal  and  vegetable  oils  for  cylinder  lubrication.  Such  an 
oil  is  a  compound  of  a  fatty  acid  and  glycerine.  When  exposed 
to  a  high  temperature  the  fatty  acid  and  the  glycerine  become 
separated.  If  a  substance  such  as  soda  or  potash  is  present, 
the  fatty  acid  combines  with  it  and  forms  soap.  This  process  is 
called  saponification.  If,  however,  no  such  substance  is  present 
the  acid  will  be  free  to  attack  other  substances  as  it  may  be  able. 
Fatty  acids  attack  iron  feebly,  but  if  long  continued  the  result 
may  be  a  serious  corrosion,  resulting  in  the  formation  of  what  is 
known  as  an  iron  soap.  The  temperature  within  the  cylinders  and 
boilers  was  quite  sufficient  to  thus  decompose  the  oil,  and  there 
would,  under  such  circumstances,  be  set  free  in  the  boilers  an 
amount  of  fatty  acid  depending  on  the  amount  of  oil  used  in  the 
cylinders  and  finding  its  way  into  the  condenser  and  feed-water. 
There  were  thus  present  all  the  conditions  necessary  for  the 
corrosion  of  the  interior  of  boilers  by  fatty  acids,  and  many  seri- 
ous cases  were  laid,  in  part  at  least,  to  this  cause.  These  trou- 
bles appeared  especially  with  the  introduction  of  the  surface 
condenser,  and  the  part  which  fatty  acids  might  play  being  un- 
derstood, the  use  of  animal  and  vegetable  oils  for  the  lubrication 
of  the  cylinders  was  abandoned,  and  in  their  place  hydrocarbon 
or  mineral  oils  are  now  used.  Such  oils  are  derived  as  one  of 
the  constituents  of  crude  petroleum,  and  are  not  compounds  of 
a  fatty  acid  and  glycerine.  They  are  compounds  of  carbon  and 
hydrogen,  and  belong  to  an  entirely  different  class  of  chemical 
substances.  They  do  not  produce  a  fatty  acid  on  being  heated, 
and  cannot,  at  least  directly,  take  part  in  the  process  of  boiler 
corrosion. 

In  modern  practice,  therefore,  nothing  but  the  best  hydro- 
carbon oil,  entirely  free  from  animal  or  vegetable  admixture, 
should  be  used  for  cylinder  lubrication.  With  lubricant  of  this 
character  modern  boilers  should  be  free  from  corrosion  charge- 
able to  the  action  of  fatty  acids. 

These  are,  however,  not  the  only  acids  which  have  given 
trouble  in  the  way  of  boiler  corrosion.  Under  certain  circum- 
stances free  hydrochloric  or  muriatic  acid  is  found  in  boilers. 
This  is  presumably  due  to  the  breaking  up  of  magnesium 
chloride,  forming  hydrochloric  acid  and  magnesium  hydrate. 
The  most  dangerous  feature  of  the  corrosion  due  to  hydro- 
chloric acid  is  that  under  conditions  which  may  exist  within 
steam  boilers  the  chloride  of  iron  first  formed  may  become 


312  PRACTICAL  MARINE  ENGINEERING. 

broken  up,  giving  rise  to  other  neutral  compounds  of  iron,  and 
setting  free  the  acid  to  continue  its  ravages. 

There  are  also  possibilities  of  the  development  of  nitric  acid 
from  the  organic  matter  which  in  small  quantities  may  occa- 
sionally find  its  way  into  steam  boilers. 

Except  as  it  may  be  modified  by  electro-chemical  action, 
the  presence  of  such  an  acid  usually  results  in  a  general  surface 
corrosion,  at  least  of  all  surfaces  not  protected  by  a  sufficient 
layer  of  lime  scale. 

The  most  troublesome  feature  of  boiler  corrosion  has  not 
been,  however,  a  general  or  more  or  less  uniformly  distributed 
effect,  such  as  would  naturally  be  charged  to  the  action  of  an 
acid  diffused  throughout  the  boiler.  It  has  been  rather  in  the 
so-called  pitting.  This  term  refers  to  the  formation  of  small 
pits  or  depressions  from  the  size  of  a  pin  head  upward,  and 
conical  or  cup-shaped  in  form.  The  depth  of  such  pits  may  be 
anything  from  a  slight  depression  to  a  hole  cut  entirely  through 
a  boiler  tube.  They  are  found  in  no  fixed  locality,  though  more 
commonly  on  the  tubes,  furnaces,  and  combustion  chambers 
than  elsewhere.  When  found  they  are  usually  filled  with 
a  blackish  or  brownish  pasty  mass,  consisting  chiefly  of  iron 
oxide  with  a  slight  admixture  of  lime  salts,  oily  matter,  and 
other  substances.  This  deposit  within  the  pits  is  often  covered 
with  a  skin  of  somewhat  different  composition,  consisting  of 
lime  salts  and  iron  oxide  in  more  nearly  equal  proportions. 

To  account  for  the  formation  of  these  pits,  various  explana- 
tions have  been  suggested,  most  of  them  involving  electro-chemi- 
cal action  as  a  more  or  less  pronounced  feature.  To  under- 
stand the  nature  of  this  action  a  few  explanations  must  first  be 
given. 

Nearly  all  substances  are  in  a  different  electrical  condition, 
or  at  a  different  electrical  potential,  as  it  is  called.  This  differ- 
ence is  found  not  only  between  substances  of  different  kinds, 
but  also  between  similar  substances  at  different  temperatures, 
or  in  different  physical  conditions,  as,  for  example,  between  two 
pieces  of  iron  or  steel,  one  of  which  has  been  hammered  or 
worked  more  than  the  other.  Due  to  this  difference  of  elec- 
trical potential  there  is  a  tendency  to  set  up  a  flow  of  electricity 
from  one  to  the  other,  and  as  a  further  result  to  so  change  the 
two  substances  as  to  bring  them  into  electrical  equilibrium.  In 
other  words,  the  result  of  such  a  difference  of  electrical  con- 


OPERATION,  MANAGEMENT  AND  REPAIR.  313 

dition  is  always  to  bring  about  changes  which  will  cause  the  dif- 
ference to  disappear,  and  so  bring  the  two  substances  into 
equilibrium.  These  chemical  changes  of  the  two  substances, 
which  tend  toward  electrical  equilibrium,  may  be  much  helped 
or  hindered  by  the  medium  in  which  the  bodies  are  immersed. 
If  they  are  in  dry  air,  for  example,  no  such  activity  takes  place, 
and  the  difference  of  electrical  condition  continues  unchanged. 
If,  however,  they  are  immersed  in  water,  or  especially  in  salt  or 
slightly  acid  water,  the  operation  will  usually  be  much  assisted 
by  the  activity  of  the  medium  for  the  substances.  It  may  also 
happen  that  the  medium  and  substances  are  so  related  as  to 
bring  about  a  series  of  chemical  changes,  of  which  the  first  are 
those  which  would  naturally  be  associated  with  the  transfer  of 
electricity  and  the  development  of  equilibrium,  while  the  second 
counteract  these  changes  chemically,  and  bring  the  substances 
back  to  their  original  condition,  and  so  keep  them  constantly  in 
the  condition  of  electrical  difference.  There  is  as  constantly 
the  attempt  to  restore  equilibrium,  and  hence  so  long  as  these 
conditions  continue  there  will  result  this  continued  series  of 
chemical  actions,  accompanied  by  a  constant  flow  of  electricity 
from  one  substance  to  the  other.  In  order,  however,  that  this 
flow  of  electricity  may  be  thus  constant  and  so  constitute  a  cur- 
rent of  electricity,  as  it  is  termed,  there  must  be  a  path  for  a 
complete  circuit  or  flow  in  one  direction  through  the  medium 
which  produces  the  chemical  changes,  and  in  the  other  direction 
outside  of  this  medium.  The  substance  from  which  the  current 
flows  in  the  medium  is  known  as  the  electro-positive  element, 
and  the  other  the  electro-negative.  The  chemical  activity  pro- 
ceeds and  the  current  is  formed,  in  general,  at  the  expense  of 
the  electro-positive  element. 

These  operations  are  illustrated  in  the  ordinary  voltaic  cell 
or  battery,  such  as  those  used  for  ringing  bells,  etc.  In  most 
of  these  batteries,  however,  the  action  is  not  self-sustaining,  and 
if  allowed  to  continue  for  a  little  time,  a  condition  of  electrical 
equilibrium  is  reached,  or,  as  ordinarily  stated,  the  battery  is 
run  down.  In  others  used  for  telegraphy  and  other  purposes 
the  operations  are  self-sustaining  and  continuous  until  the 
chemical  substances  are  exhausted. 

In  a  boiler  these  conditions  for  a  more  or  less  continued 
electro-chemical  action  may  be  fulfilled  in  a  variety  of  ways. 
Parts  of  the  structure  of  widely  differing  temperatures  or  of 


3i4  PRACTICAL  MARINE  ENGINEERING. 

different  physical  or  chemical  compositions  may  provide  the 
elements  in  a  different  electrical  condition.  Still  more  likely 
is  such  a  difference  to  be  found  between  iron  and  its  oxides, 
especially  the  magnetic  oxide  or  mill  scale  (Fe3  O4),  or  between 
a  particle  of  carbon  in  the  steel  and  the  surrounding  metal,  or 
between  a  place  in  the  steel  where  the  proportion  of  carbon  is 
much  greater  than  the  average  and  the  surrounding  metal,  or 
between  a  bit  of  slag  or  other  impurity  in  wrought  iron  and  the 
surrounding  metal.  Copper,  either  in  the  form  of  oxide,  or  es- 
pecially in  the  metallic  form,  would  also  supply  a  substance  dif- 
fering strongly  from  the  iron.  The  exciting  liquid  is  the  water 
in  the  boiler,  and  its  action  will  be  more  vigorous  according  as 
it  is  more  acid  in  reaction,  higher  in  temperature,  and  denser  in 
concentration.  With  a  high  pressure  boiler,  water  of  high 
density  and  quite  acid  in  character,  and  with  the  usual  lack  of 
homogenity  or  uniformity  in  the  structure  of  the  boiler,  we 
should,  therefore,  expect  the  effects  of  electro-chemical  action 
to  be  shown  in  marked  degree.  It  happens,  furthermore,  that 
iron  is  electro-positive  to  copper,  to  carbon,  and  to  its  own 
oxides,  so  that  in  all  cases  likely  to  occur  the  operation  will 
proceed  at  the  expense  of  the  iron.  . 

From  the  very  nature  of  these  electro-chemical  actions 
their  effects  are  necessarily  local  in  character,  and  so  far  as 
understood  they  seem  to  provide  a  fairly  good  explanation  of 
the  formation  of  pits  as  already  described.  It  is  not  unlikely, 
however,  that  in  some  cases  they  are  due  rather  to  simple 
chemical  action,  and  that  their  localization  to  a  small  spot  is 
due  to  special  or  accidental  causes,  such  as  the  protection  of  the 
surrounding'metal  by  lime  scale,  or  a  peculiar  weakness  against 
chemical  attack  at  that  point,  due  to  peculiarities  in  chemical  or 
physical  structure. 

The  possibility  of  deposits  of  copper  on  boiler  surfaces  has 
been  already  mentioned.  These  were  first  noted  in  connection 
with  the  corrosion  accompanying  the  general  introduction  of 
the  surface  condenser.  It  was  believed  that  the  copper  of  the 
condenser  tubes  was  attacked  by  the  pure  water  resulting  from 
the  condensation  of  the  steam,  or  by  the  fatty  acids  formed  as 
above  explained,  and  was  then  carried  over  into  the  boiler  and 
deposited  on  the  surfaces.  To  prevent  such  action  the  con- 
denser tubes  were  tinned,  thus  covering  the  copper  from  the 
action  of  the  water  or  the  fatty  acids.  Neither  this  step  nor 


OPERATION,  MANAGEMENT  AND  REPAIR.  315 

the  substitution  of  hydrocarbon  oil  for  that  containing  fatty 
acids  has  made  any  very  marked  difference  in  boiler  pitting,  and 
at  the  most  the  presence  of  the  copper  can  have  been  only  one 
among  a  number  of  causes  as  suggested. 

There  has  been  much  difference  of  opinion  and  difference 
in  experience  regarding  the  question  whether  wrought  iron  or 
steel  boiler  tubes  were  the  more  liable  to  corrosion.  It  was 
pointed  out  that  wrought  iron  was  less  homogeneous  than  steel, 
and  therefore  the  latter  should  be  the  better.  The  early  experi- 
ence with  steel  hardly  bore  out  this  claim,  and  in  fact  the  gen- 
eral opinion  seems  to  have  been  that  wrought  iron  tubes  were 
found  to  corrode  less  readily  than  steel.  In  explanation  of  this, 
it  may  be  said  that  while  wrought  iron  was  less  homogeneous 
physically,  the  steel  was  perhaps  less  homogeneous  chemically, 
and  in  any  event  contained  a  larger  proportion  of  carbon  than 
the  iron,  so  that  it  would  by  no  means  follow  that  it  would  neces- 
sarily be  less  subject  to  electro-chemical  action.  The  latest  and 
best  products  of  the  steel  makers  for  such  purposes,  however, 
are  extraordinarily  low  in  carbon  and  very  homogeneous,  and 
experience  with  such  grades  of  material  seems  to  show  them 
superior  to  wrought  iron  in  this  respect. 

We  have  thus  developed  in  some  detail  the  causes  of  corro- 
sion on  the  water  side  of  steam  boilers,  so  far  as  they  are  under- 
stood. For  the  prevention  of  such  effects  their  causes  must  be 
removed  or  counteracted. 

For  reducing  the  amount  of  oxidation  and  the  possible  re- 
sults due  to  electro-chemical  action,  the  presence  of  air  in  the 
feed  water  must  be  avoided  by  preventing  as  far  as  possible  the 
entrance  of  water  from  overboard  into  the  feed.  The  hot-well 
or  feed-tank  should  also  be  of  good  size  and  kept  full,  so  that 
there  may  be  no  danger  of  its  getting  too  low7  from  time  to  time, 
and  thus  allowing  the  pump  to  take  air.  The  piston  rod  on  the 
low-pressure  cylinder  should  be  kept  well  packed,  so  as  to  pre- 
vent the  entrance  of  air  during  the  exhaust  part  of  the  stroke. 
The  feed  pump  rods  on  the  water  end  should  be  kept  well  packed 
for  the  same  reason. 

To  prevent  acid  corrosion  the  formation  of  the  acids  must 
be  prevented  as  far  as  possible,  and  such  as  may  form  must  be 
neutralized  within  the  boiler.  The  prevention  of  the  formation 
of  fatty  acids  has  been  considered  above.  We  have  also  seen 
that  the  formation  of  other  acids  is  due  chiefly  to  the  presence 


3i6  PRACTICAL  MARINE  ENGINEERING. 

of  salts  contained  in  sea  water,  or  to  organic  substances.  We 
have  therefore  simply  an  additional  reason  for  keeping  all  such 
substances  out  of  the  boiler  as  far  as  possible.  To  neutralize  such 
acid  as  may  form,  bicarbonate  of  soda,  or  soda-ash,  as  it  is 
known  in  the  trade,  may  be  used  from  time  to  time,  and  in  such 
quantities  as  may  be  found  necessary.  To  test  the  water  for 
acidity  the  litmus  test  is  used.  Blue  litmus  paper  turns  red  when 
dipped  in  water  slightly  acid,  while  if  the  water  is  alkaline  it  re- 
mains blue,  or  the  red  color  caused  by  an  acid  is  changed  to 
blue.  By  this  means  the  condition  of  the  water  may  be  tested 
from  time  to  time  and  soda  used  accordingly.  Care  must  be 
taken  not  to  use  it  in  too  great  excess,  as  it  may  cause  foaming. 
The  soda  is  introduced  by  means  of  a  soda  cock  on  the  con- 
denser. Instead  of  keeping  the  water  alkaline  by  the  use  of 
soda,  dependence  is  often  placed  on  the  zinc  slabs  used  to  pre- 
vent electro-chemical  corrosion.  These  are  gradually  dissolved, 
forming  zinc  chloride,  and  this  will  undoubtedly  tend  to  neutral- 
ize free  acids  and  to  keep  the  water  alkaline.  Whether  sufficient 
or  not,  can  of  course  be  readily  determined  by  the  litmus  test 
before  referred  to. 

For  the  prevention  of  electro-chemical  action  the  causes 
must  also  be  removed  or  neutralized  as  far  as  possible.  This 
cannot  be  realized  entirely,  but  it  is  clear  that  the  results  will  be 
the  better,  as  the  following  conditions  are  the  more  nearly  ful- 
filled : 

(1)  The  structure  of  the  boiler  should  be  of  material  as 
homogeneous  as  possible  in  its  chemical  constitution  and  physi- 
cal condition. 

(2)  Causes  liable  to  produce  oxidation  or  the  presence  of 
foreign  substances  should  be  kept  out  of  the  boiler  as  far  as 
possible. 

(3)  The  water  in  the  boiler  should  be  made  as  nearly  neu- 
tral or  non-exciting  relative  to  the  iron  as  possible.     This  in  a 
general  way  will  be  attained  by  keeping  it  slightly  alkaline  rather 
than  acid,  and  by  avoiding  very  high  densities. 

In  addition  to  these  means  for  reducing  the  causes,  there 
remains  one  further  step,  and  that  is : 

(4)  The  provision  of  a  substance  which  shall  be  electro- 
positive to  iron,  and  readily  attacked,  so  that  the  activity  will  be 
diverted  from  the  iron  to  the  protecting  substance,  and  the 
operation  will  proceed  at  the  expense  of  the  latter  rather  than 


OPERATION,  MANAGEMENT  AND  REPAIR.  317 

of  the  former.    Such  a  substance  we  find  in  zinc,  and  its  use  for 
this  purpose  is  very  general  and  seemingly  beneficial. 

It  may  be  also  noted  that  the  formation  of  zinc  chloride  as 
referred  to  in  the  foregoing  will  aid  in  keeping  the  water  alkaline 
in  reaction,  thus  reducing  its  natural  activity,  and  contributing 
further  to  the  general  decrease  of  electro-chemical  action. 

In  order  to  be  effective  as  a  protection  to  the  iron  in  the  man- 
ner described,  the  zinc  must  be  in  actual  metallic  contact  with 
the  structure  of  the  boiler.  It  is  usually  in  the  form  of  rolled  or 
cast  slabs,  weighing  8  to  12  Ibs.  each.  These  are  often  placed  in 
perforated  sheet  metal  baskets  hung  from  the  stays  or  attached 
to  other  portions  of  the  boiler.  Where  the  basket  is  attached  to 
the  boiler  there  should  be  bright  metal  contact,  and  the  attach- 
ment should  be  by  screwed  joint  or  other  equivalent  means,  so 
that  the  separation  of  the  two  surfaces  by  the  formation  of  scale 
or  corrosion  between  them  may  be  prevented.  The  zinc  should 
also  be  connected  to  the  basket  by  through  bolts  or  other  means 
which  will  insure  continuous  metallic  contact.  In  some  cases 
the  zincs  are  hung  by  a  through  bolt  without  other  means  of  sup- 
port. In  such  case,  as  the  zinc  becomes  used  it  may  fall  apart  and 
the  pieces  may  lodge  where  they  will  obstruct  the  circulation,  or 
be  otherwise  undesirable.  In  any  event,  they  will  no  longer  pro- 
tect the  part  of  the  boiler  confided  to  their  care,  and  their  period 
of  usefulness  may  therefore  be  less  than  when  supported  and 
connected  to  a  basket,  as  described  above.  The  number  of  zincs 
fitted  varies  greatly,  according  to  the  judgment  of  different  engi- 
neers. In  some  cases  not  more  than  10  or  12  would  be  assigned 
to  the  protection  of  a  large  double-end  boiler,  while  in  others  as 
many  as  40  or  50  would  be  used.  The  latter  number  is  the  bet- 
ter representative  of  good  modern  practice.  In  any  case  they 
should  be  distributed  as  nearly  uniformly  as  possible  throughout 
the  boiler,  in  order  that  the  latter  may  be  thus  subdivided  into 
parts,  each  more  especially,  under  the  influence  of  a  given  slab. 

In  connection  with  the  use  of  zinc  it  may  be  noted  that  for 
such  boilers  as  may  be  used  for  distilling  purposes,  that  is,  for 
the  provision  of  fresh  water  for  drinking  and  cooking,  the  zincs 
should  be  omitted,  as  the  presence  of  any  considerable  amount 
of  zinc  chloride  will  render  the  water  unsuitable  for  such  uses. 

Instead  of  depending  on  zinc  to  prevent  or  divert  electro- 
chemical action,  as  above  described,  some  engineers  prefer  to 
depend  simply  on  reducing  the  activity  of  the  water  by  keeping 


318  PRACTICAL  MARINE  ENGINEERING. 

it  alkaline  by  the  use  of  soda,  introduced  as  the  litmus  test  may 
show  to  be  necessary. 

When  spots  are  found  in  a  boiler,  showing  the  presence  of 
pronounced  corrosion,  they  should  be  cleaned  off  thoroughly, 
washed  with  soda  solution,  and,  if  not  on  a  heating  surface,  cov- 
ered with  a  thin  wash  of  Portland  cement.  This  will  attach  itself 
to  the  iron  and  protect  it  in  a  manner  similar  to  the  lime  scale. 

The  beneficial  effect  of  scale  in  thus  protecting  the  surfaces 
of  boilers  from  corrosion  is  well  recognized,  and  there  is  no 
doubt  that  its  presence  as  a  thin  wash  or  layer  is  of  great  value. 
In  order  to  be  effective,  however,  it  must  be  so  firmly  and  closely 
attached  to  the  iron  as  to  prevent  contact  of  the  water  with  the 
surface,  else  the  corrosive  action  may  proceed  under  the  scale 
and  result  all  the  more  seriously  because  it  is  protected  from  in- 
spection until  the  scale  is  thoroughly  removed.  On  the  tubes 
and  other  heating  surfaces  of  the  boiler,  with  their  changes  of 
temperature  and  consequent  expansions  and  contractions,  the 
scale  is  especially  liable  to  be  cracked  off  or  partially  separated 
from  the  iron,  with  possible  results,  as  here  noted.  This  is  still 
more  likely  to  be  the  case  as  the  scale  becomes  thicker  and  the 
metal  more  liable  to  become  overheated.  It  has  also  been  sug- 
gested that  a  very  heavy  scale  may  result  in  an  overheating  of 
the  metal  sufficient  to  decompose  the  moisture  present,  thus  lib- 
erating oxygen  and  forming  the  magnetic  oxide  of  iron  or  black 
mill  scale  (Fe3  O4).  This  is  highly  electro-negative  to  iron,  and 
thus  it  may  give  rise  to  harmful  electro-chemical  reactions. 

Laying  Up  Boilers. — When  boilers  are  to  be  laid  up,  the  prin- 
ciples already  explained  will  indicate  the  nature  of  the  means 
suitable  for  preventing  corrosion. 

On  the  outside,  paint  or  other  like  coating  may  be  used,  as 
already  noted.  On  the  fire  side  of  water-tube  boilers  protec- 
tion is  sometimes  gained  by  building  a  slow  fire  of  tar  or  resin- 
ous material,  the>  tarry  smoke  from  which  condenses  on  the 
tubes  and  furnishes  protection  from  the  air  with  its  moisture  and 
carbon  dioxide.  Use  is  also  made  of  quicklime  in  trays  renewed 
from  time  to  time.  This  absorbs  the  moisture  and  so  keeps  the 
air  dry. 

On  the  inside,  all  boilers  when  laid  up  should  be  either 
empty  or  entirely  full.  If  a  boiler  stands  for  any  considerable 
length  of  time  partly  full,  corrosion  is  likely  to  occur  about  the 
water  line.  If  they  are  to  be  out  of  use  for  a  short  time  only, 


OPERATION,  MANAGEMENT  AND  REPAIR.  319 

they  may  be  filled  full  of  water  made  slightly  alkaline  by  the  ad- 
dition of  soda,  the  condition  of  the  water  being  determined  by 
the  litmus  test  already  referred  to.  If  they  are  to  be  laid  up  for 
a  longer  time  it  is  better  to  lay  them  up  dry.  To  this  end  the 
water  is  removed,  the  manhole-plates  taken  off  and  the  interior 
thoroughly  dried  out  by  the  introduction  of  trays  of  burning 
charcoal  or  coke.  The  boiler  is  then  closed  up,  except  a  lower 
manhole,  through  which  a  tray  of  freshly  burning  charcoal  is  in- 
troduced, and  the  manhole  cover  is  put  on.  The  charcoal  will 
consume  most  of  the  remaining  oxygen,  and  the  boiler  will  thus 
be  protected.  Instead  of  the  final  introduction  of  a  tray  of  char- 
coal, trays  of  quicklime  may  be  used  to  insure  the  absence  of  all 
moisture,  and  the  boiler  then  closed  as  before. 

It  is  readily  seen  that  these  various  methods  are  simply 
ways  of  carrying  out  the  necessary  conditions  for  preventing 
oxidation,  as  already  discussed,  and  if  these  principles  are  kept 
clearly  in  view  the  means  most  conveniently  at  hand  may  be 
suitably  adapted  to  provide  the  protection  desired. 

Sec.  41.    BOILER  SCAI,E. 

It  is  well  known  that  sea  water  contains  in  solution  a  certain 
amount  of  solid  matter,  while  even  ordinary  fresh  water  is  not 
wholly  free  from  similar  substances.  As  long  as  the  water  re- 
mains in  its  natural  condition  these  solids  remain  in  solution ; 
but  under  the  change  of  condition  to  which  the  water  in  a  steam 
boiler  is  subjected,  they  are  liable,  as  explained  later  in  detail,  to 
separate  out  from  the  water  and  thus  to  form  scale  or  sludge, 
according  as  the  circumstances  may  determine. 

The  proportion  of  the  solid  matter  in  ordinary  sea  water  is 
about  (by  weight)  i  part  in  32,  or  1-32.  This  is  the  same  as 
about  5  oz.  per  gallon,  or  2  Ibs.  per  cu.  ft.  The  solid  matter  con- 
sists chiefly  of  chloride  of  sodium  or  common  salt,  with  small 
quantities  of  calcium  sulphate  and  carbonate,  magnesium  sul- 
phate and  chloride,  with  smaller  quantities  of  other  substances. 
An  average  composition  of  this  solid  matter  is  about  as  follows  : 

Chloride  of  Sodium  (common  salt) 76  per  cent. 

Chloride  of  Magnesium 10 

Sulphate  of  Magnesium 6 

Sulphate  of  Calcium  (gypsum) 5        " 

The  remaining  3  per  cent  consists  of  small  quantities  of 
other  salts  with  a  little  organic  matter. 

The  proportion  of  the  solid  matter  in  river  and  lake  water  is 


32o  PRACTICAL  MARINE  ENGINEERING. 

quite  variable  with  the  locality,  and  no  representative  or  average 
analysis  can  be  given.  The  amount  held  in  solution  may  vary 
from  perhaps  10  to  250  parts  in  100,000  or  from  .015  oz.  to  .30 
oz.  per  gallon,  or  .1  oz.  to  2.5  oz.  per  cu.  ft.  It  is  composed 
chiefly  of  the  carbonates  of  calcium  and  magnesium  with  smaller 
quantities  of  the  sulphates  of  calcium  and  magnesium,  and  other 
substances.  In  addition  to  the  substances  in  solution,  quanti- 
ties of  sand,  mud,  organic  matter,  etc.,  may  be  carried  in  sus- 
pension, dependent  entirely  on  the  locality  and  special  circum- 
stances. 

Boiler  scale  from  sea  water  is  composed  chiefly  of  calcium 
sulphate  or  sulphate  of  lime,  as  it  is  commonly  called,  while  that 
from  fresh  river  or  lake  water  is  composed  chiefly  of  calcium 
carbonate  or  carbonate  of  lime,  as  commonly  called.  With 
brackish  water,  as  we  might  expect,  the  proportions  of  the  two 
are  more  nearly  the  same.  Following  are  analyses  of  boiler  scale 
by  Professor  Lewes  which  may  be  considered  as  typical  of  the 
incrustations  formed  by  river  water,  brackish  water  and  sea 
water,  respectively : 

CONSTITUENTS.  RIVER. 

Calcium  Carbonate 75-85 

Calcium  Sulphate 3-68 

Magnesium  Hydrate 2. 56 

Sodium  Chloride 0.45 

Silica 7.66 

Oxides  of  Iron  and  Alumina 2.96 

Organic  Matter 3.64 

Moisture 3.20 


100.00  100.00         100.00 

It  thus  appears  that  scale  from  river  water  may  be  looked 
on  as  an  impure  calcium  carbonate,  that  from  sea  water  as  an 
impure  calcium  sulphate,  while  that  from  brackish  water,  as  we 
should  expect,  is  a  mixture  of  the  two  in  more  nearly  equal  pro- 
portions. 

Sodium  chloride  or  common  salt  is  soluble  in  water  until 
the  proportion  exceeds  some  25  or  30  per  cent.  This  corre- 
sponds to  a  density  of  8  or  10  on  the  usual  hydrometer,  and  is  far 
greater  than  that  reached  by  the  water  in  marine  boilers.  This 
substance  therefore  gives  no  trouble  so  far  as  helping  to  form 
scale  is  concerned,  and  the  small  amount  found  in  analysis  of 
boiler  scale  is  probably  due  to  the  shutting  in,  so  to  speak,  of  a 
small  amount  of  water  during  the  formation  of  the  scale.  In 
discussing  the  formation  of  boiler  scale  for  our  present  purposes, 


OPERATION,  MANAGEMENT  AND  REPAIR.  321 

it  will  be  sufficient  to  refer  to  the  behavior  of  the  salts  of  calcium 
and  magnesium. 

Calcium  carbonate  (CaCO3)  is  practically  insoluble  in  water, 
while  calcium  bicarbonate  (CaC2  O5)  is  quite  soluble,  and  it  is  in 
this  form  that  the  substance  exists  in  solution  in  water.  If  r?ow 
the  \\ater  is  heated  to  the  boiling  point  carbonic  acid  (CO2)  is 
driven  away  from  the  bicarbonate,  it  becomes  reduced  to  the 
simple  carbonate,  and  being  now  insoluble  it  separates  out  a?  a 
more  or  less  powdery  deposit.  Mixed  with  other  salts,  how- 
ever, especially  calcium  sulphate,  or  if  there  is  a  little  sulphuric 
acid  in  the  water,  it  may  collect  on  the  heating  surfaces  and 
form  a  hard  and  closely  adhering  scale.  Magnesium  bicarbonate 
is  in  a  similar  manner  reduced  to  the  simple  carbonate,  which  is 
insoluble,  and  is  then  deposited  in  the  same  fashion. 

Calcium  sulphate  is  soluble  in  cold  water  to  a  slight  extent, 
as  found  in  sea  water.  As  the  water  is  heated,  however,  or  as 
the  density  becomes  greater,  the  proportion  of  sulphate  which  it 
can  retain  in  solution  becomes  less  and  less.  When  the  tempera- 
ture rises  to  280°  or  290°  (corresponding  to  from  35  to  45  Ibs. 
gauge  pressure)  the  water  can  no  longer  retain  any  of  the  sul- 
phate in  solution,  and  it  is  all  deposited.  It  is  also  largely  de- 
posited, even  at  a  temperature  of  212°,  if  the  density  rises  to 
3-32  or  above.  The  other  sulphates  become  likewise  insoluble 
and  are  completely  deposited  if  the  temperature  rises  to  about 
350°  or  over,  corresponding  to  about  120  Ibs.  gauge  pressure.' 
These  sulphates  of  lime  and  magnesium  thus  deposited  tend  to 
attach  themselves  to  the  surfaces  within  the  boiler,  and  to  form 
a  very  hard  and  crystalline  scale. 

As  to  the  effects  of  this  scale,  its  presence  in  a  very  thin 
layer  is  often  considered  beneficial  as  a  protection  to  the  surface 
of  the  boiler  from  corrosive  influences.  On  the  other  hand,  how- 
ever, it  is  a  much  poorer  conductor  of  heat  than  metal,  and  its 
presence  on  the  heating  surfaces  retards  the  transmission  of  heat 
from  the  fire  through  to  the  water.  In  the  extreme  case  the  heat 
may  be  so  effectually  shut  off  from  the  water  that  it  simply  be- 
comes banked  up,  so  to  speak,  in  the  metal,  and  in  this  way  the 
tubes  and  other  heating  surfaces  may  become  seriously  over- 
heated with  resulting  damage  to  the  boiler.  The  scale  may  also 
in  extreme  cases  become  so  collected  between  the  tubes  or  be- 
tween the  combustion  chamber  and  boiler  sheets  as  to  impede 
the  circulation  of  the  water  and  thus  lead  to  overheating  and  its 


322  PRACTICAL  MARINE  ENGINEERING. 

dangers,  as  referred  to  above.  In  water-tube  boilers  the  accu- 
mulation of  scale  on  the  inside  of  the  heating  tubes  is  of  special 
danger,  as  the  circulation  becomes  in  such  case  rapidly  ob- 
structed and  the  danger  of  overheating  and  rupture  is  corre- 
spondingly increased.  In  a  similar  manner  the  accumulation  of 
scale  in  the  interior  of  tubular  feed-water  heaters  rapidly  de- 
creases their  efficiency  as  heaters,  if  no  worse  results  follow 
due  to  the  burning  out  of  coils,  or  to  the  resulting  shortness  of 
water  in  the  boilers. 

Scale  Prevention,  Fresh  Water. — The  only  sure  way  of  pre- 
venting scale  is  simply  to  keep  it  out  of  the  boiler.  If  the  scale- 
forming  substances  find  entrance  to  the  boiler  it  will  be  found 
very  difficult  to  prevent  its  formation,  at  least  to  some  extent. 

On  boats  navigating  inland  waters  the  jet  condenser  is  still 
for  the  most  part  used,  the  feed  is  ordinarily  taken  from 
the  condenser,  and  therefore  practically  from  overboard. 
In  such  boilers,  therefore,  we  may  expect  the  formation  of  the 
usual  fresh  water  scale,  consisting  chiefly  of  calcium  carbonate. 
For  the  treatment  of  fresh  water  scale  a  great  variety  of  methods 
have  been  proposed.  In  some  cases  the  substances  proposed  act 
chemically,  in  others  mechanically.  From  the  great  variation  in 
the  character  of  the  solid  matter  contained  in  fresh  water,  it  can 
hardly  be  expected  that  any  one  method  of  treatment  or  sub- 
stance will  prove  equally  good  in  all  cases. 

If  a  feed-water  heater  is  used,  and  is  effective  in  heating 
the  water,  it  will  be  found  that  most  of  the  scale  will  be  deposited 
in  the  heater,  especially  if  it  is  of  sufficient  size  to  allow  of  proper 
time.  In  this  way  the  scale  may  be  kept  out  of  the  boiler  proper. 
The  heater,  .however,  should  be  so  made  as  to  readily  admit  of 
cleaning,  especially  if  the  water  contains  any  considerable  pro- 
portion of  scale-forming  salts,  otherwise  it  will  soon  become 
choked  and  ineffective. 

Among  the  various  substances  which  have  been  recom- 
mended for  the  prevention  of  fresh  water  scale  the  following 
may  be  mentioned : 

Oak  and  hemlock  bark  and  other  like  substances  which 
contain  tannic  acid  are  more  or  less  effective  in  waters  contain- 
ing carbonates  of  calcium  or  magnesium.  The  tannic  acid,  how- 
ever, will  attack  the  iron  of  the  boiler  and  may  lead  to  serious 
corrosion. 

Molasses,  cane  juice,  fruits,  distillery  slops,  vinegar  and 


OPERATION,  MANAGEMENT  AND  REPAIR.  323 

other  like  substances  containing  acetic  acid  have  also  been  used 
with  success  where  no  sulphates  are  present.  The  acetic  acid, 
however,  is  still  more  injurious  to  the  iron  than  the  tannic  acid, 
and  the  organic  substances  will  form  a  scale  with  sulphates  if 
they  are  present. 

Sal-ammoniac  when  used  with  a  feed  water  containing  cal- 
cium carbonate  brings  about  an  exchange  between  the  two  sub- 
stances as  a  result  of  which  ammonium  carbonate  and  calcium 
chloride  are  formed.  The  former  of  these  is  soluble  and  quite 
volatile  and  passes  off  mostly  with  the  steam.  The  latter  is  quite 
soluble  and  thus  the  deposition  of  the  calcium  carbonate  is 
avoided.  This  operation  by  itself,  however,  would  result  in  the 
gradual  accumulation  of  calcium  chloride  in  the  boiler,  thus  rais- 
ing the  density  of  the  water  to  a  point  where  ultimately  it  would 
begin  to  deposit.  This  condition  may,  of  course,  be  controlled 
by  a  suitable  use  of  the  blow. 

Tanate  of  soda  is  well  recommended  for  general  use,  but 
with  water  containing  sulphates  a  small  amount  of  soda-ash 
should  be  added. 

Among  the  substances  which  act  mechanically,  crude  petro- 
leum and  kerosene  oils  are  probably  the  most  widely  used.  The 
latter  may  be  recommended  as  the  better  of  the  two,  as  the  crude 
oil  will  sometimes  aid  in  scale  formation.  They  seem  to  act  best 
in  cases  where  there  are  some  sulphates  present,  as  in  slightly 
brackish  water,  or  in  the  waters  of  certain  geographical  regions. 
Kerosene  seems  to  act  by  preventing  the  particles  of  scale  from 
sticking  closely  together  or  from  tightly  adhering  to  the  heating 
surfaces,  so  that  much  of  the  matter  will  collect  as  a  sludge  in 
the  bottom  of  the  boiler,  and  that  on  the  heating  surfaces  will  be 
more  easily  removed. 

In  all  cases  where  there  is  reason  to  expect  the  accumula- 
tion in  the  bottom  of  the  boiler  of  deposits  thrown  down  in  a 
loose  or  powdery  form,  the  bottom  blow  should  be  freely  used 
so  as  to  prevent  the  accumulation  of  too  great  a  quantity,  or  op- 
portunity for  its  hardening  into  scale. 

In  spite  of  all  modes  of  treatment  there  will  be  found  some 
scale  on  the  heating  surfaces,  and  provision  must  be  made  for 
entering  the  boiler  and  removing  it  with  appropriate  tools  as  the 
occasion  demands  and  circumstances  permit. 

In  many  of  our  inland  waters  the  amount  of  scale-forming 
substances  is  so  small  that  no  special  treatment  is  thought  neces- 


324  PRACTICAL  MARINE  ENGINEERING. 

sary,  and  little  attention  is  paid  to  the  matter  except  to  remove 
the  accumulation  at  the  periods  of  regular  inspection  and  over- 
haul. 

Scale  Prevention,  Salt  Water. — Turning  now  to  boilers  in 
which  sea  water  may  form  a  portion  of  the  feed,  it  will  be  of  in- 
terest to  first  note  briefly  the  historical  development  of  the  mod- 
ern situation. 

In  the  early  days  of  marine  engineering,  the  temperature 
and  pressure  of  the  steam  were  low,  and  the  jet  condenser  was 
in  general  use.  The  feed  water  which  was  drawn  from  the  min- 
gled condensing  water  and  condensed  steam  was  but  slightly 
fresher  than  sea  water,  so  that  large  amounts  of  solid  matter 
were  thus  fed  into  the  boiler.  In  consequence  the  density  would 
have  risen  rapidly  had  it  not  been  kept  down  by  blowing  off  a 
part  of  the  water  in  the  boiler  of  relatively  high  density  and  re- 
placing it  with  the  salt  feed  of  lower  density.  Had  the  sulphates 
of  calcium  and  magnesium  thus  brought  into  the  boiler  been 
completely  deposited,  enormous  quantities  of  scale  would  have 
been  formed,  and  this  method  of  operation  would  have  been 
quite  impracticable.  Due,  however,  to  the  moderate  pressure 
then  in  use  and  to  the  fact  that  the  density  was  kept  usually  be- 
tween i  3-4  and  2,  the  salts  were  held  fairly  well  in  solution,  and 
but  a  moderate  amount  of  scale  was  deposited. 

As  steam  pressures  advanced,  however,  beyond  40  or  45 
Ibs.,  conditions  were  reached  under  which  first  the  calcium  sul- 
phate and  later  magnesium  sulphate  and  other  salts  are  com- 
pletely deposited.  Under  such  circumstances  blowing  off  to  re- 
duce the  density  of  the  water  will  only  make  matters  so  much 
the  worse,,  for  the  lower  the  density  is  to  be  maintained  the 
greater  must  be  the  amount  blown  off,  and  hence  the  greater  the 
amount  of  extra  feed,  and  the  greater  the  amount  of  scale  form- 
ing salts  brought  into  the  boiler,  all  of  which  will  be  deposited. 

It  became  therefore  necessary  to  abandon  the  use  of  the  jet 
condenser  and  salt  feed.  Its  place  was  taken  by  the  modern  sur- 
face condenser.  So  long  as  this  condenser  is  perfectly  tight  the 
feed  water  consists  of  the  condensed  steam,  and  is  therefore  al- 
most perfectly  fresh  water.  Due,  however,  to  steam  leaks  at  the 
various  joints,  seams  and  glands,  to  the  occasional  use  of  the 
steam  whistle,  and  to  the  use  of  steam  in  certain  auxiliaries  from 
which  it  is  not  returned  to  the  condenser,  there  will  be  a  con- 
tinual shortage  in  the  feed  water  which  under  usual  conditions 


OPERATION,  MANAGEMENT  AND  REPAIR.  325 

will  be  found  between  say  2  and  5  per  cent.  Until  recent  years 
this  shortage  was  made  up  by  the  use  of  sea  water  obtained 
usually  by  opening,  as  circumstances  required,  the  salt  water 
cock  connecting  the  salt  water  side  of  the  condenser  with  tne 
steam  side.  It  is  very  difficult  to  keep  the  tubes  oi  a  surface 
condenser  packed  perfectly  tight,  and  in  some  cases  the  con- 
denser was  allowed  to  run  a  little  leaky,  simply  to  make  up  in 
this  way  the  salt  feed  required. 

Due  to  this  admixture  of  salt  feed,  the  scale  forming  salts 
of  which  are  all  deposited  in  the  boiler,  there  will  be  a  gradual 
formation  of  scale  greater  or  less,  according  to  the  length  of  the 
run  and  the  proportion  of  salt  feed  make  up. 

In  recent  years  experience  has  clearly  shown  that  the  dan- 
gers of  overheating  and  the  general  bad  effects  due  to  the  pres- 
ence of  scale  are  more  and  more  pronounced  as  the  pressures 
are  higher.  It  has  become  therefore  more  and  more  important 
to  prevent  so  far  as  possible  the  entrance  of  any  sea  water  into 
the  boiler,  and  thus  avoid  the  formation  of  scale  with  its  troubles 
and  dangers.  To  this  end,  in  modern  practice,  the  make  up  feed 
is  provided  by  an  evaporator,  or  in  some  cases  by  feeding  one 
boiler  with  salt  feed  and  thus  restricting  the  scale  formation  to 
this  boiler,  while  the  condensed  steam  from  all  the  boilers  is  re- 
turned to  the  other  ones  as  feed.  In  all  such  cases  it  will  be 
noted  that  this  scheme  amounts  to  a  transfer  of  the  use  of  salt 
water  and  the  formation  of  scale  from  the  boilers  in  general  to 
the  evaporator,  or  to  the  particular  boiler  in  which  it  is  allowed 
to  accumulate. 

For  short  trips  as,  for  example,  those  met  with  in  bay,  har- 
bor or  channel  service,  or  on  short  coasting  voyages,  fresh  water 
for  make  up  feed  may  be  carried  in  tanks  instead  of  providing  it 
by  means  of  an  evaporator.  By  many  engineers  this  is  consid- 
ered the  preferable  method  whenever  tanks  of  sufficient  size 
can  be  provided,  and  in  some  cases  with  the  double  bottom  style 
of  construction,  double  bottoms  have  been  utilized  to  a  consid- 
erable extent  for  this  purpose. 

It  is  rare  that  the  condenser  can  be  maintained  perfectly 
tight,  so  that  even  under  the  best  practicable  conditions  there  is 
apt  to  be  some  passage  of  sea  water  into  the  steam  side  of  the 
condenser,  and  thence  into  the  boiler.  Under  the  best  condi- 
tions the  amount  of  scale  formed,  however,  is  so  small  that  com- 
monly no  special  treatment  is  attempted,  and  the  scale  is  allowed 


326  PRACTICAL  MARINE  ENGINEERING. 

to  deposit,  and  is  then  removed  at  the  regular  periods  of  inspec- 
tion and  overhaul. 

Some  attempts  have  been  made  to  prepare  sea  water  by  the 
removal  of  the  calcium  sulphate  in  a  separate  vessel  before  en- 
tering the  boiler.  This  may  be  done  by  the  use  of  sodic  fluoride 
which  causes  the  sulphate  to  separate  out  and  settle  to  the  bot- 
tom as  a  fine  powder.  The  remaining  water  is  practically  free 
from  this  substance  and  may  be  used  for  boiler  feed  without  fear 
of  causing  scale. 

Soda  ash  and  other  alkalies  have  sometimes  been  used  in 
boilers,  with  feed  water  containing  sulphate  of  lime.  They  act 
by  converting  the  sulphate  into  a  carbonate,  and  thus  into  a 
somewhat  less  objectionable  form. 

Barium  chloride  acts  in  a  somewhat  similar  fashion  by  pro- 
ducing barium  sulphate  and  calcium  chloride. 

The  use  of  zinc  in  boilers  is  also  by  many  believed  to  prevent 
to  some  extent  the  formation  of  scale  by  the  reaction  of  the  alka- 
line zinc  chloride  on  the  scale  forming  salts. 

With  sea-going,  as  with  inland  boilers,  the  bottom  blow 
should  be  used  occasionally  and  as  the  particular  circumstances 
may  demand,  so  as  to  remove  the  accumulation  of  such  sub- 
stances as  may  be  thrown  down  as  a  powder  or  sludge  and  thus 
collect  in  the  bottom  of  the  boiler. 

However  careful  the  provisions  for  keeping  sea  water  out 
of  the  boilers  or  no  matter  what  methods  may  be  used  to  pre- 
vent scale  formation,  it  is  almost  sure  to  gradually  accumulate, 
and  assurance  of  safety  from  the  troubles  and  dangers  which 
may  result  can  only  be  obtained  from  periodical  examination 
and  scaling  as  may  be  found  necessary.  All  marine  boilers  must, 
of  course,  be  provided  with  manhole  plates  for  this  purpose,  and 
the  internal  arrangement  of  tubes,  braces,  furnaces,  etc.,  should 
be  made,  so  far  as  possible,  with  a  view  to  furthering  this  neces- 
sary operation. 

Combinations  of  Oil  and  Scale. — We  have  thus  far  referred 
to  scale  formed  simply  from  the  solid  matter  in  the  feed  water. 
The  combinations  which  may  be  formed  by  the  deposited  salts 
and  oil  from  the  cylinders  as  it  may  enter  with  the  feed  water 
are,  however,  of  even  still  greater  importance,  and  must  now  be 
noted. 

Oil  coming  in  thus  with  the  feed  water  is  caught  by  the  cir- 
culating currents  and  distributed  more  or  less  throughout  the 


OPERATION,  MANAGEMENT  AND  REPAIR.  327 

bailer,  though  by  reason  of  its  lesser  weight  it  will  tend  grad- 
ually to  rise  and  accumulate  as  a  scum  at  the  surface  of  the 
water.  In  thus  wandering  about,  a  drop  may  come  in  contact 
with  a  bit  of  solid  matter  separated  from  the  water.  The  two 
join  together,  the  oil  forming  a  coating  about  the  sulphate,  and 
they  journey  on  meeting  and  joining  with  other  like  particles.  The 
combination  of  the  oil  and  sulphate  may  have  about  the  same 
specific  gravity  as  the  water  in  the  boiler,  and  hence  these  parti- 
cles will  readily  move  with  the  circulating  currents,  either  up  or 
down,  as  they  happen  to  be  flowing.  They  are  thus  swept  along 
the  heating  surfaces,  to  which  they  attach  themselves  all  the 
more  readily  by  reason  of  their  oily -covering,  and  on  either  the 
upper  or  lower  side  as  they  happen  to  be  moving  with  a  down 
or  up-flowing  current.  In  this  way  the  coating  gradually  in- 
creases until  it  has  attained  a  thickness  sufficient  to  seriously 
interfere  with  the  passage  of  the  heat. 

In  other  cases,  when  the  scale  and  oil  are  lighter  or  the 
water  is  denser  and  heavier,  there  seems  to  be  formed  at  the 
surface  of  the  water  in  the  boiler  a  kind  of  oil  and  scale  blanket 
or  layer  floating  about,  and  perhaps  ultimately  by  the  gradual 
increase  of  weight  sinking  and  covering  some  portion  of  the 
heating  surface.  Especially  is  this  oil  "pancake,"  as  it  has  been 
called,  liable  to  settle  should  the  density  of  the  water  in  any  way 
be  suddenly  decreased.  Still  otherwise  should  the  boiler  be 
blown  down  by  the  bottom  blow,  such  an  oil  blanket  would 
naturally  settle  and  attach  itself  to  some  part  of  the  heating  sur- 
face. Should  the  boiler  be  then  filled  again,  the  coating  would 
remain  where  attached.  This  shows  that  under  such  circum- 
stances a  boiler  should  never  be  blown  down  with  the  bottom 
blow  without  first  using  thoroughly  the  surface  blow  to  remove 
as  far  as  possible  all  such  accumulations  of  oil  or  of  oil  and 
scale  from  the  surface  of  the  water. 

The  danger  to  be  feared  from  this  combination  of  scale  and 
oil  is  not  in  its  close  adherence  to  the  surfaces,  but  in  its  non- 
conductivity  for  heat.  Experiments  show  that  1-16  to  1-8  inch 
of  such  a  covering  is  far  worse  in  this  respect  than  perhaps  1-2 
inch  or  more  of  scale  alone.  The  danger  to  be  feared  is  there- 
fore overheating  and  collapse,  and  not  a  few  cases  of  the  col- 
lapse of  furnaces  and  other  parts  of  marine  boilers  are  believed 
to  be  due  to  this  cause. 

So  far  as  these  effects  are  concerned  it  is  seen  that  it  is  bet- 


328  PRACTICAL  MARINE  ENGINEERING. 

ter  to  carry  a  high  density  in  the  boilers  than  a  low  one,  so  as 
to  keep  such  oil  and  scale  combinations  at  the  surface  of  the 
water,  where  they  may  be  disposed  of  by  the  surface  blow. 

As  it  is  practically  impossible  to  prevent  the  entrance  of 
some  scale-forming  materials  into  the  boiler,  the  danger  of 
trouble  with  oil  and  scale  combinations  is  most  surely  pre- 
vented by  keeping  the  oil  out.  To  this  end  a  cylinder  oil  should 
be  used  having  a  high  point  of  vaporization,  as  the  higher  this 
point  the  smaller  the  amount  carried  into  the  condenser.  Of 
this  oil  the  minimum  amount  necessary  should  be  used  in  the 
cylinders,  and  the  feed  water  should  be  filtered  to  remove  what- 
ever oil  it  may  contain. 

Sec.  42.    BOII/ER  OVERHAULING  AND  REPAIRS. 

[i]  Inspection  and  Test. 

We  will  suppose  that  after  some  considerable  term  of  serv- 
ice, and  preparatory  to  a  general  overhauling,  a  battery  of 
boilers  are  to  be  carefully  and  thoroughly  examined.  The 
more  important  points  may  now  be  considered. 

(1)  Furnace  Fronts. — The  furnace  fronts  and  doors  may  be 
found  warped  and  cracked,  and  if  this  is  the  case  to  such  an  ex- 
tent as  to  interfere  with  the  proper  closure  of  the  furnaces,  or 
with  the  proper  and  convenient  care  of  the  fires,  the  necessary  re- 
pairs or  renewals  should  be  made. 

(2)  Grates  and  Bearers. — The  grate  bars  will  often  be  found 
warped  and  twisted,  or  badly  burned,  and  at  various  points  sunk- 
en below  or  sprung  above  their  proper  level.    Such  irregularities 
in  the  grate  may  occasion  loss  of  coal  at  some  points,  while  they 
will  further  the  accumulation  of  ash  and  clinker  at  others,  and 
will  make  it  almost  impossible  to  give  to  a  fire  the  proper  atten- 
tion, or  to  get  from  a  square  foot  of  grate  surface  the  power 
which  it  should  be  able  to  give.    The  bearers  may  also  be  the 
cause  of  trouble  by  warping  or  settling  from  having  been  over- 
heated, and  all  of  these  points  must  be  attended  to  before  the 
boiler  can  be  considered  again  ready  for  proper  service. 

(3)  Bridge-wall — The  bridge-wall  is  liable  to  be  found  more 
or  less  burnt  out  and  dilapidated,  while  on  the  front  side  clinker 
and  bits   of  brick  may  be  found   fused  together  in   irregular 
masses.    All  of  this  must  be  removed  and  the  bridges  built  up 
again  with  fresh  bricks  to  the  proper  height  as  referred  to  in 
Sec.  38  [i]. 


OPERATION,  MANAGEMENT  AND  REPAIR.  329 

(4)  Tubes. — The  tubes  will,  of  course,  be  swept  and  properly 
cleaned  on  the  fire  side.    The  existence  of  small  leaks  must  be 
carefully  looked  for,  the  evidence  being  the  presence  of  soot  and 
scale  burned  to  the  metal  where  the  water  has  come  through 
and  evaporated.    The  back  and  front  tube  sheets  and  the  inside 
of  the  tubes  must  be  carefully  examined  for  any  such  evidence. 
Signs  of  especial  wear  should  also  be  looked  for  at  the  back 
ends  of  the  tubes,  and  if  ferrules  are  used  some  will  probably  be 
found  so  worn  and  burned  out  as  to  require  renewing. 

In  water-tube  boilers  any  special  warping  or  change  in  the 
shape  or  curvature  of  the  tubes  should  be  carefully  noted,  as  it 
may  indicate  overheating  due  to  faulty  circulation  caused  by  a 
clogging  of  the  tube  by  scale  and  sediment.  A  split  or  badly 
ruptured  tube  will,  of  course,  show  itself  by  the  resulting  leak, 
but  in  a  water-tube  boiler  such  leak  may  be  very  difficult  to 
locate  without  the  removal  of  several  of  the  tubes  in  the  vicinity 
of  the  one  giving  the  trouble.  These  points  depend  entirely  on 
the  type  and  style  of  construction,  and  no  general  rule  can  be 
given  for  definitely  and  immediately  locating  such  a  tube  in  a 
water-tube  boiler. 

(5)  Joints  and  Seams. — The  joints  and  seams  throughout  the 
boiler,   both   in  the   combustion   chamber  and   on   the   outside, 
should  be  carefully  examined  for  small  leaks,  either  between  the 
plates  or  about  the  rivets.    If  the  leakage  is  not  serious,  caulking 
will  serve  as  a  sufficient  remedy.     In  other  cases,  however,  the 
removal  of  old  rivets  and  the  insertion  of  new  ones  may  be 
found  necessary. 

(6)  Front  Connections  and  Uptakes. — The  front  connections, 
uptakes  and  fittings  should  be  examined  to  make  sure  that  the 
plates  are  not  warped  or  broken  from  their  fastenings,  and  that 
the  dampers  and  their  operating  gear  are  in  proper  condition. 

(7)  Fittings. — The  valves  and  cocks  are  likely  to  be  found 
more   or  less  worn  on  their  seats  and  leaky  in   consequence. 
These  will  require  regrinding  and  refitting,  or  replacing  by  new 
where  necessary.     The  operating  gear,  such  as  valve  spindles, 
wheels,  levers,  chains,  gear-wheels,  etc.,  should  be  examined  for 
any  breakage  or  derangement  of  parts.    The  various  joints  and 
fittings  about  the  steam  and  water  pipes  must  also  be  examined 
for  signs  of  leaks,  distress,  corrosion,  or  other  derangement. 

(8)  Bracing. — The  manhole  plates  will,  of  course,  have  been 
removed  to  facilitate  examination  of  the  interior. 


330  PRACTICAL  MARINE  ENGINEERING. 

The  braces,  especially  where  pin  joints  and  like  connections 
are  used,  should  be  carefully  examined  for  defects  in  the  con- 
nections and  fittings,  and  also  for  any  symptoms  of  buckling  or 
distress  in  the  braces  themselves. 

(9)  Scale.  The   scale  present  in  the  boiler   should  be   ex- 
amined as  to  its  amount,  distribution  and  character — whether 
hard  or  soft,  greasy  or  otherwise,  closely  adhering  or  readily 
cracked  off.    Accumulation  of  scale  between  the  tubes  or  screw 
stays,  and  of  scale  and  sludge  in  the  bottom  of  the  boiler  must 
also  be  looked  for  and  noted.     In  some  cases  an  oily  or  greasy 
coating  with  little  or  no  mineral  matter  and  forming  a  coating 
over  the  scale  and  on  the  heating  surfaces  may  be  observed. 
This  will  indicate  large  quantities  of  oil  in  the  boiler,  and  insuffi- 
cient use  of  the  surface  blow. 

(10)  Corrosion. — It  is,  of  course,  of  the  highest  importance 
to  examine  carefully  for  signs  of  corrosion  and  pitting  through- 
out the  interior  of  the  boiler.    The  following  locations,  however, 
are  those  in  which  it  is  most  apt  to  be  found : 

On  the  sheets  at  and  near  the  water  line.  Occasionally  also 
severe  corrosion  is  found  in  the  steam  spaces. 

On  the  braces  near  the  water  line. 

On  the  tubes  and  combustion  chamber  tops. 

On  the  furnaces  near  the  grate  level. 

The  nature  and  distribution  of  this  corrosion  must  be  care- 
fully noted,  in  order  that  the  most  suitable  steps  may  be 
taken  for  its  arrest  and  prevention  in  the  future.  When  they 
can  be  gotten  at,  corroded  spots  may  be  scraped  and  scrubbed 
clean  with  water  made  alkaline  by  the  addition  of  soda  or  weak 
lye,  and  if  not  on  a  heating  surface,  a  redistribution  of  the  zincs 
may  prove  of  service,  while  in  general  a  more  careful  attention 
to  the  various  means  suggested  in  Sec.  40  may  be  recommended. 
The  zincs  and  their  fittings.,  as  discussed  in  Sec.  40,  must  also  be 
carefully  looked  after.  Many  of  the  zincs  will  probably  be  found 
to  have  wasted  away  to  only  a  small  part  of  their  original  size, 
and  to  have  become  changed  in  physical  structure  to  a  blackish 
or  brownish  crumbly  or  brittle  mass.  In  some  cases  remnants 
of  the  slabs  may  be  found  lodged  between  the  tubes  and  screw 
stays,  and  often  more  or  less  covered  or  imbedded  in  deposits 
of  scale. 

On  the  exterior  of  the  boiler  the  points  most  liable  to 
corrosion  are  on  the  fronts  about  the  bottom  where  damp  ashes 


OPERATION,  MANAGEMENT  AND  REPAIR.  331 

may  have  lain,  or  about  the  saddles  and  on  the  under  side  where 
dampness  and  water  are  liable  to  be  formed.  Thorough  clean- 
ing, followed  by  a  coat  of  paint,  asphaltum  varnish,  or  other 
like  material,  is  the  usual  remedy  in  such  cases,  at  least  where 
its  application  is  practicable. 

Before  the  application  of  any  such  coating,  the  plates  should 
be  thoroughly  dried,  else  it  will  be  of  little  use.  The  presence 
of  moisture  on  the  plates  causes  the  especial  difficulty  connected 
with  the  effective  application  of  paint  in  such  places,  and  where 
convenient  the  use  of  a  portable  sheet-iron  drying  stove  contain- 
ing burning  charcoal  or  coke  may  be  found  of  use.  This  may 
be  placed  under  the  surfaces  to  be  covered  so  as  to  furnish  an 
ascending  current  of  warm  air,  thus  aiding  in  keeping  them  dry 
during  the  application  of  the  paint. 

For  the  structural  material  in  bilges  and  bunkers  a  coating 
of  Stockholm  tar  put  on  hot  and  then  sprinkled  with  Portland 
cement  is  highly  recommended  by  some  engineers. 

(n)  Manholes  and  Covers. — The  faces  on  which  the  manhole 
cover  joints  are  made  should  be  examined  for  corrosion  or 
scale,  or  anything  which  may  affect  their  evenness,  or  make 
difficult  the  fitting  of  a  tight  joint. 

(12)  Drill  Test. — Where  the  boiler  has  seen  long  service,  or 
where  there  are  evidences  of  serious  corrosion,  or  doubt  exists 
as  to  the  thickness  or  quality  of  the  plates,  they  must  be  drilled 
at  such  points  as  may  be  selected.    In  this  way  the  thickness  of 
the  remaining  good  metal   may  be   ascertained,   and   the   safe 
pressure  to  be  carried  may  be  fixed  in  accordance  with  the  evi- 
dence thus  found. 

(13)  Hydraulic  Test. — When  the  boiler  has  been  overhauled 
and  put  in  proper  condition,  at  least  as  far  as  anything  which 
may  affect  its  strength  is  concerned,  the  hydraulic  test  may  be 
applied.    To  this  end  the  boiler  is  filled  full  of  water  and  pres- 
sure is  put  on,  usually  by  means  of  a  special  pump  connected 
for  the  purpose.    The  test  pressure  is  usually  one  and  one-half 
times  the  working  pressure  desired.     It  is  considered  that  this 
pressure  is  not  sufficient  to  seriously  try  or  injure  the  boiler 
should  it  be  properly  constructed,  and  of  suitable  factor  of  safety 
throughout,  while  at  the  same  time  it  will  be  sufficient  to  de- 
velop small  leaks,  and  should  the  boiler  be  unduly  weak  at  any 
point,  the  bulging  or  yielding  or  distress  at  such  point  should 
become  apparent.     If  no  such  evidences  appear,  then  it  is  con- 


332  PRACTICAL  MARINE  ENGINEERING. 

sidered  that  the  boiler  is  abundantly  strong  for  the  working 
pressure  as  desired. 

To  prepare  the  boiler  for  the  test  the  springs  should  be 
withdrawn  from  the  safety  valves  and  lengths  of  pipe  of  suitable 
size  substituted,  so  that  the  valves  may  be  screwed  down  fast. 
All  stop  valves  and  gauge  glass  connections  should  then  be 
tightly  closed,  as  well  as  the  connection  to  any  pressure  gauge 
which  will  not  indicate  up  to  the  test  pressure. 

While  the  test  is  under  way  the  boiler  is  subjected  to  the 
most  careful  examination,  both  inside  and  out.  The  furnaces, 
combustion  chambers  and  back  tube-sheets  are  examined  from 
the  inside,  and  the  shell  and  its  various  joints  and  seams  from 
the  outside.  Small  leaks  are  watched  for  and  stopped  by  caulk- 
ing, if  possible,  or  if  about  the  tube  ends,  by  re-expanding.  Es- 
pecial care  must  also  be  had  in  watching  for  any  signs  of  bulging, 
buckling  or  other  deformation  or  distress. 

Where  the  test  is  to  be  carried  out  with  especial  care,  ex- 
tension and  compression  gauges  are  provided  in  the  furnaces 
and  combustion  chambers,  and  at  other  points,  as  may  be  de- 
sired. These  serve  to  indicate  and  to  measure  the  actual  amount 
of  distortion  which  results  from  the  gradually  increasing  pres- 
sure. If  the  distortion  or  bulging  at  any  point  should  become 
abnormal,  the  pressure  should  be  relieved  by  letting  off  a  little 
water,  in  order  to  see  if  any  permanent  set  has  been  made. 
The  continuance  of  the  test  should  then  be  made  to  depend 
upon  the  behavior  of  the  part  showing  this  relative  weakness. 
For  a  thoroughly  satisfactory  test,  all  gauges  should  return  to 
the  original  setting  when  the  pressure  is  removed,  showing  no 
permanent  set  at  these  points.* 

It  will  usually  be  found  very  difficult  to  so  tighten  the  vari- 
ous valves  that  there  will  be  no  leakage.  An  idea  of  the  amount 
of  leakage  may  be  obtained  by  watching  the  rapidity  with  which 
the  pointer  on  the  pressure  gauge  moves  backward  when  the 
pump  is  stopped,  as  well  as  by  the  amount  of  pumping  required 
to  maintain  the  pressure  at  its  full  value.  The  pressure  gauge 
pointer  will  also  frequently  indicate  by  its  more  or  less  sudden 
movement  backward,  the  sudden  development  of  leaks  about 
the  riveted  joints  or  tube  ends. 

It  has  sometimes  been  urged  against  the  hydraulic  test  that 
it  may  severely  strain  some  part  of  the  boiler  where  the  yield 
or  distress  is  difficult  to  observe,  and  thus  so  weaken  it  that  a 


OPERATION,  MANAGEMENT  AND  REPAIR.  333 

further  yield  or  rupture  may  occur  under  a  much  smaller,  load 
at  a  later  time.  The  hydraulic  test  is,  however,  very  generally 
employed  both  in  the  naval  and  mercantile  marines,  and  if  care- 
fully conducted  and  with  a  pressure  not  exceeding  one  and  one- 
half  times  the  working  pressure,  it  is  not  likely  that  harm  will 
result,  while  the  test  will  develop  the  small  leaks  and  minor 
defects,  and  may  be  the  means  of  exposing  serious  faults  of 
workmanship  or  design. 

The  same  test  is,  of  course,  applied  to  new  boilers  as  a 
final  preliminary  to  the  getting  up  of  steam. 

In  some  cases  the  water  test  has  been  carried  out  by  filling 
the  boiler  and  then  lighting  wood  fires  within  the  furnaces.  The 
expansion  of  the  water  will  furnish  the  increase  of  pressure  de- 
sired, which  may  be  eased  by  the  safety  or  stop  valve,  as  neces- 
sary. It  has  been  claimed  that  the  boiler  being  in  this  way 
heated,  was  more  nearly  in  its  regular  service  condition.  While 
this  may  be  so  to  a  slight  extent,  the  boiler  is,  nevertheless,  far 
from  regular  service  condition,  and  the  method  has  the  serious 
disadvantage  that  it  does  not  allow  examination  of  the  furnaces, 
combustion  chambers  and  back  tube  sheets  while  it  is  under 
way.  It  is  also  under  less  ready  control  than  the  pump  method, 
and  is  now  but  rarely  employed. 

BOILER    REPAIRS. 

In  the  following  suggestions  regarding  boiler  repairs  we 
shall  refer  more  especially  to  such  as  may  become  necessary  at 
sea  or  under  emergency  conditions,  rather  than  to  those  which 

may  result  in  the  course  of  a  thorough  overhauling  in  port. 

i 
(2)  leakage  from  the  Joints  of  Boiler  Mountings. 

Such  leakage  by  soaking  through  the  lagging  and  keeping 
the  plates  wet  may  give  rise  to  surface  corrosion  on  the  boiler 
shell. 

The  first  care  must  be  to  stop  the  leakage  by  screwing 
down,  re-caulking  or  re-making  the  joints,  as  may  be  necessary. 

If  there  is  reason  to  suspect  corrosion  of  the  boiler  as  well, 
the  lagging  should  be  removed  and  the  corroded  surfaces 
scraped  clean  and  painted  with  good  metal  paint  or  other  suit- 
able covering. 

(3)  Leakage  About  Shell  Joints. 

Usually  caulking  will  be  sufficient  to  stop  any  ordinary 
small  leak  in  these  joints.  If  it  is  serious  and  caulking  gives 


334  PRACTICAL  MARINE  ENGINEERING. 

but  Jittle  improvement,  it  may  indicate  a  loose  rivet  or  one  with 
the  head  gone.  In  such  case  leakage  about  the  rivet  will  usually 
be  present  also,  and  will  thus  serve  to  locate  the  trouble.  Such 
rivet  must,  of  course,  be  replaced,  in  order  to  effectually  stop 
the  leak. 

Where  a  rivet  has  blown  out  and  a  quick  repair  is  desired, 
the  hole  may  be  drilled  or  reamed  true  and  then  tapped  out. 
Then  fit  a  bolt  with  corresponding  thread  and  cut  it  partly 
through  near  the  root  with  a  hack  saw.  Screw  this  in,  knock 
off  the  projecting  end,  rivet  down  the  remainder  and  the  job 
is  complete. 

In  some  cases  instead  of  replacing  loose  or  broken  rivets, 
or  where  for  other  reasons  caulking  seems  to  be  inefficient  in 
stopping  the  leak,  it  may  be  considered  desirable  to  put  a  patch 
over  the  seam,  rivets  and  all.  In  such  case  a  so-called  "soft- 
patch"  is  applied.  This  is  illustrated  in  Fig.  204.  The  patch 
is  flanged  and  made  with  a  recess  of  suitable  size  and  form  to 
accommodate  the  rivet  points.  It  is  then  filled  with  a  stiff  putty 


TUT 

Fig.  204.     Patch  for  Leaky  Joint. 

of  red  lead  and  secured  by  bolts  as  shown.  Such  an  application 
is  really  a  red-lead  poultice,  kept  in  place  by  a  suitably  formed 
steel  cover,  and  secured  to  the  shell,  as  explained.  It  is  un- 
necessary to  make  such  a  patch  of  metal  more  than  3-16  or  J4 
inch  thick,  since  it  is  not  intended  to  add  strength  to  the  shell, 
but  simply  to  keep  the  red-lead  putty  in  place,  and  thus  stop 
the  jet  of  leaking  steam  or  water. 

The  chief  difficulty  with  leaks  in  the  shell  seams  and  with 
the  outside  of  boilers  in  general  arises  from  the  trouble  in  sub- 
jecting them  to  the  proper  examination  due  to  the  presence  of 
the  lagging.  As  usually  fitted,  this  covering  is  difficult  of  re- 
moval, and  small  leaks  thus  covered  in  may  continue  for  long 
periods  of  time,  keeping  the  outer  surfaces  wet  and  causing 
rust  and  corrosion  where  its  existence  may  not  be  expected. 
A  form  of  boiler  lagging  admitting  of  ready  renewal  and  re- 
placement in  sections  is  much  to  be  desired,  and  if  full  advantage 
were  taken  of  such  a  form  of  covering  to  keep  closer  watch  of  all 


OPERATION,  MANAGEMENT  AND  REPAIR.  335 

joints  on  the  outer  surface,  much  trouble  might  be  avoided  by 
taking  the  first  appearances  of  trouble  in  time. 

(41  I/eakage  at  Internal  Joints. 

The  internal  joints,  on  the  whole,  give  more  trouble  than 
those  on  the  outside.  This  is  only  to  be  expected  due  to  the 
thinner  plates,  the  enormous  range  of  temperature  differences 
which  exist,  and  the  resultant  expansions  and  contractions.  The 
difference  in  expansion  between  the  furnaces  and  tubes  is  es- 
pecially liable  to  give  trouble  with  the  joints  connecting  the 
furnace  to  the  combustion  chamber,  and  several  varieties  of 
joint  have  been  proposed  to  reduce  this  trouble  to  a  minimum. 
With  a  joint  such  as  shown  in  Fig.  43,  the  greater  expansion  of 
the  furnace  tends  directly  to  open  up  the  joint,  while  with  that 
shown  in  Fig.  9  the  result  is  a  shear  on  the  rivets  but  no  direct 
tendency  to  open  the  plates.  In  the  latter  case,  however,  the 


Soft  Patch. 


Locomotive  Patch. 


Hard  Patch. 
Fig.  205.     Different  Forms  of  Patches. 

rivets  are  more  directly  exposed  to  the  fire  than  in  the  former, 
and  thus  the  points  between  the  two  joints  are  very  nearly 
balanced.  The  joint  of  Fig.  9,  however,  allows  a  more  ready  re- 
moval of  the  furnace,  and  on  this  account  it  is  often  selected 
rather  than  that  of  Fig.  43. 

Leaky  joints  on  the  combustion  chamber  should  be  first 
carefully  re-caulked.  This  operation,  however,  cannot  be  car- 
ried on  indefinitely,  for  after  caulking  to  a  certain  extent,  the 
edge  must  be  chipped  off  to  get  a  fresh  caulking  edge.  This, 
if  repeated,  will  leave  the  metal  between  the  rivets  and  edge  too 
narrow  for  safety.  If  careful  and  judicious  caulking  does  not 
remedy  leaks  in  these  seams,  it  is  evident  that  the  rivets  need 
renewal,  and  in  carrying  this  out  especial  care  should  be  taken 
to  see  that  the  holes  are  fair  in  the  two  plates,  and  that  the 
rivets  fill  them  completely. 


336  PRACTICAL  MARINE  ENGINEERING. 

(5)  Patches. 

We  may  now  turn  more  especially  to  the  patching  of 
boilers  and  to  the  different  kinds  of  patches  employed. 

We  must  first  remember  as  a  general  principle  that  any 
thickening  of  metal  on  the  heating  surfaces  is  undesirable  and 
to  be  avoided  as  far  as  possible,  or  reduced  to  the  lowest  possible 
extent.  If,  therefore,  a  patch  on  a  heating  surface  is  to  be 
considered  as  a  permanent  fixture,  the  faulty  metal  should  be 
cut  out,  thus  doubling  the  thickness  only  over  the  necessary 
width  for  the  fastenings.  A  patch  put  on  in  this  way  with  rivets 
headed  up  as  in  regular  boiler  work  is  known  as  a  hard  patch, 
and  is  illustrated  in  Fig.  205.  In  some  cases  the  patch  must 
be  put  on  from  one  side  only,  or  is  more  temporary  in  character. 
In  such  case  either  the  locomotive  or  the  soft  patch  is  used. 
The  former  is  a  patch  put  on  with  tap  bolts,  as  illustrated  in  Fig. 
205,  and  usually  without  cutting  out  the  metal.  The  soft  patch 
has  been  already  referred  to.  In  its  more  usual  form,  as  shown 
in  Fig.  205,  it  is  made  by  lipping  down  a  plate  of  steel  so  as  to 
contain  and  hold  in  place  a  coating  or  layer  of  red-lead  putty. 
It  is  more  suitable  for  temporary  repairs,  or  where  the  sur- 
faces are  so  rough  and  uneven  that  a  patch  of  the  other  forms 
could  not  be  fitted.  The  soft  patch  is  sometimes  secured  with 
tap  bolts,  and  sometimes  with  through  bolts  and  nuts,  as  may  be 
most  convenient  with  the  case  in  hand. 

As  to  whether  a  patch  should  be  put  on  the  water  or  fire 
side,  much  will  depend  on  location  and  convenience.  Where 
it  is  possible  the  water  side  may  be  chosen  so  that  the  steam 
pressure  will  tend  to  keep  the  patch  in  place.  Usually,  however, 
the  fire  side  of  the  plate  is  more  easily  gotten  at,  and  in  many 
cases  there  is  no  choice  but  to  put  the  patch  upon  this  side.  In 
any  event  with  either  the  hard  or  locomotive  patches,  the  edge 
will  require  careful  caulking  as  the  final  closure  and  making  of 
the  joint.  With  the  soft  patch,  caulking  the  edge  is  not  neces- 
sary, as  the  putty  is  depended  upon  to  stop  the  leak,  and  the 
office  of  the  patch  is  merely  to  hold  it  in  place. 

(6)  Cracks  and  Holes. 

A  small  crack  is  usually  treated  by  drilling  a  hole  at  each 
end  to  prevent  its  extension,  and  then  covering  with  a  patch, 
according  to  location  and  convenience.  Very  small  cracks  are 
sometimes  drilled  and  tapped  out  as  close  together  as  the  holes 


OPERATION,  MANAGEMENT  AND  REPAIR.  337 

will  stand,  and  then  filled  with  soft  iron  or  steel  bolts,  riveted 
down  so  as  to  overlap  and  thus  completely  close  the  crack. 

Small  isolated  holes  not  accompanied  by  a  general  thinning 
of  the  metal  may  be  treated  in  a  similar  fashion  by  drilling  and 
tapping  out  the  hole  and  riveting  in  a  bit  of  soft  iron  or  steel 
bolt.  Larger  holes,  or  where  many  are  located  near  each  other, 
or  where  they  are  accompanied  by  pronounced  thinning  of  the 
metal  must  be  treated  by  patching. 

In  general  it  may  be  noted  that  plugging  as  above  de- 
scribed, is  only  suitable  for  the  mere  stopping  of  a  leak,  and 
that  it  adds  nothing  whatever  to  the  strength  of  the  plate.  If, 
then,  the  conditions  are  such  as  to  make  additional  strength  de- 
sirable, a  patch  must  be  fitted. 

Where  a  crack  is  found  in  a  tube  sheet  it  usually  extends 
from  tube  to  tube.  Such  a  crack  may  be  covered  by  a  patch  ex- 


Fig.  206.    Patch  for  Boiler  Tube  Sheet. 

tending  over  the  crack  and  taking  enough  good  metal  to  obtain 
a  secure  hold.  The  patch  must  have  holes  cut  in  it,  of  course, 
to  correspond  to  the  tube  ends  as  shown  in  Fig.  206. 

[7]  Blisters  and  Laminations. 

With  modern  boiler  material  these  defects  are  happily  rare. 
In  former  years,  and  especially  with  iron  plates,  they  were  only 
too  frequently  met  with  as  referred  to  in  Sec.  5.  The  chief  dan- 
ger from  these  defects  is  due  to  the  weakening  of  the  plates  and 
the  liability  of  overheating,  due  to  poorer  conductivity  for  heat. 
Such  defects  if  very  small  are  often  left  undisturbed,  with  care- 
ful watching  and  measurement  from  time  to  time.  If  small  and 
the  metal  quite  thin  on  one  side,  the  thinner  part  was  cut  away, 
leaving  the  thicker  side  to  do  duty  for  both.  In  some  cases  also 
a  dog  and  supporting  bolt  was  fitted  to  support  the  remaining 
metal.  For  some  serious  cases,  however,  it  was  usually  con- 


338  PRACTICAL  MARINE  ENGINEERING. 

sidered  preferable  to  cut  out  the  metal  thus  affected,  and  cover 
the  hole  with  a  patch. 

In  all  cases  where  patches  are  put  on,  or  in  general  where 
new  material  is  put  into  the  boiler,  it  is  well,  if  convenient,  to 
select  it  of  stock  as  nearly  like  the  boiler  as  possible  in  physical 
and  chemical  constitution.  This  will  tend  to  decrease  the  pos- 
sible sources  of  electro-chemical  action  as  discussed  in  Sec.  40. 

[8]  Tubes. 

The  repairs  to  boiler  tubes  comprise  re-expanding,  plug- 
ging, and  renewal. 

Expanding  has  been  explained  in  Sec.  16,  and  a  repetition 
of  the  process  may  be  required  from  time  to  time,  to  keep  the 
tube  ends  tight.  The  immediate  cause  of  the  leakage  of  boiler 
tubes  is  often  the  accumulation  of  dirt  and  scale  about  the  tube 
ends  and  on  the  tube  sheet.  These  points  should  therefore  be 
carefully  looked  after,  or  the  re-expanding  will  be  of  little  use. 
Care  must  be  taken  that  the  operation  of  re-expanding  is  not 
repeated  too  often,  or  the  metal  of  the  tube  end  may  become  so 
thinned  and  hardened  that  there  will  be  danger  of  weakness  or 
brittleness  at  this  point. 

For  stopping  a  tube  which  has  split  or  in  any  way  de- 
veloped a  serious  leak,  a  tube  stopper  or  plug  is  used.  Tem- 
porary stoppers  of  pine  wood  are  often  employed.  Such  a  plug 
closely  fitting  the  tube  and  twelve  or  fifteen  inches  long  may 
be  forced  in  from  the  front  end  to  a  point  where  it  covers  a  split 
or  hole,  and  thus  provides  a  temporary  repair.  The  swelling  of 
such  a  plug  caused  by  the  action  of  the  water  and  steam  will 
cause  it  to  stick  closely  in  place  and  thus  more  effectually  stop 
the  leak  than  would  a  metal  plug  in  the  same  location.  For  more 
permanently  plugging  a  tube,  tapered  cast  iron  plugs  are  used, 
one  at  each  end,  driven  in  to  a  tight  fit  and  held  in  place  by  a 
rod  passing  through  them  from  one  end  of  the  tube  to  the  other 
and  set  up  with  thread  and  nut.  The  plugs  and  nuts  should  be 
faced  so  that  when  set  up  with  a  copper  washer  or  turn  of  cop- 
per wire  underneath,  a  steam  tight  joint  between  the  plug  and 
nut  may  be  made.  To  plug  a  tube  in  this  manner  the  fire 
must,  of  course,  be  drawn  and  the  back  connection  entered  in 
order  to  insert  the  back  plug  in  place  and  adjust  the  rod  and  nut. 

When  a  tube  is  to  be  renewed  the  old  one  must  first  be 
drawn.  To  this  end  the  back  end  is  closed  down  so  as  to  readilv 


OPERATION,  MANAGEMENT  AND  REPAIR.  339 

pass  through  the  hole  in  the  tube  sheet.  A  rod  is  then  passed 
through  the  tube  and  a  nut  and  washer  are  fitted  to  the  back  end, 
the  washer  being  of  such  size  that  it  will  bear  on  the  tube  end 
and  at  the  same  time  will  pass  through  the  hole  in  the  tube 
sheet.  The  front  end  of  the  rod  passes  freely  through  a  dog  or 
strong-back  whose  feet  rest  on  the  tube  sheet,  and  is  provided 
with  a  nut  bearing  on  the  face  of  the  dog.  The  nut  being  then 
forced  down,  the  rod  is  withdrawn  and  with  it  the  tube.  To 
facilitate  withdrawal  the  front  end  of  the  tube  is  usually  made 
of  slightly  larger  diameter  than  the  back  end,  and  the  tube  once 
started  is  readily  withdrawn  the  remainder  of  the  way.  Before 
inserting  the  new  tube  the  metal  of  the  tube  sheets  about  the 
holes  should  be  carefully  examined  to  see  that  the  holes  are 
smooth  and  fair  and  that  no  reason  exists  why  the  expansion  of 
the  new  tube  may  not  make  a  steam  tight  joint.  The  new  tube 
may  then  be  inserted,  the  ends  expanded,  beaded  over  at  the 
back  end  or  at  the  front  and  back  ends  if  no  stay  tubes  are 
fitted,  and  the  operation  is  complete. 

[9]  Leakage  About  Stays  and  Braces. 
Leakage  at  these  points  may  be  due  to  corrosion  about  the 
joint,  or  to  loosening  due  to  repeated  expansion  and  contraction, 
or  to  bending  or  distortion  of  the  plate  or  stay  caused  by 
bulging  or  partial  collapse  of  the  plate.  If  the  leak  is  not  serious, 
setting  up  on  the  nut,  or  caulking  about  the  joint  between  stay 
and  plate  may  prove  sufficient.  If  not  it  will  usually  be  neces- 
sary to  remove  and  refit  the  stay.  For  screw-stay  bolts  this  will 
usually  require  the  reaming  out  and  retapping  of  the  holes  for 
the  next  larger  size.  For  braces  fitted  with  nuts  or  nuts  and' 
washers,  the  same  size  can  usually  be  replaced,  but  especial 
care  should  be  taken  to  insure  the  proper  smoothness  and  fair- 
ness of  surface  about  the  holes,  as  well  as  the  proper  fit  and  ad- 
justment of  the  nuts  and  washers,  so  that  the  usual  fitting  will 
provide  tightness  of  joint. 

[10]  Bulging  or  Partial  Collapse  of  Furnace  or  Combustion 
Chamber  Plates. 

We  have  already  discussed  in  Sec.  38  the  causes  of  bulging 
or  collapse,  and  the  steps  most  suitable  to  insure  immediate 
safety.  When  the  time  comes  for  examination  and  repair  the 
following  steps  may  be  taken. 

If  the  bulge  is  quite  small  it  may  be  decided  to  leave  it  un- 


340  PRACTICAL  MARINE  ENGINEERING. 

disturbed,  assuming  that  its  strength  is  practically  as  great  as 
before.  In  such  case,  however,  a  template  should  be  fitted  to  the 
bulge,  and  this  should  be  applied  from  time  to  time  in  order  to 
detect  any  signs  of  further  yielding  at  this  point. 

In  other  cases  special  girder  or  through  braces  may  be  fitted 
to  support  the  bulged  portion,  the  details  of  the  arrangement 
depending,  of  course,  wholly  on  the  circumstances  of  the  injury. 

In  other  cases  the  bulged  part  may  be  more  or  less  com- 
pletely forced  back  into  place.  This,  however,  is  an  operation 
requiring  both  skill  and  care,  and  should  not  be  undertaken 
without  making  the  preparations  necessary  to  carry  it  out  in 
the  proper  manner. 

A  portable  grate  or  furnace  for  burning  coke  or  charcoal  is 
first  provided  of  such  shape  and  with  such  arrangements  that 
the  burning  fuel  may  be  brought  close  up  to  the  bulged  surface. 
An  artificial  draft  may  be  provided  by  means  of  a  blower  from 
a  hand  forge  fitted  with  a  suitable  conduit,  or  otherwise  as  may 
be  most  convenient.  In  the  meantime  a  cast-iron  former  block 
should  be  provided,  shaped  on  its  face  to  correspond  to  the  sur- 
face of  the  plate  when  forced  back  into  position.  A  hydraulic 
jack  or  other  like  appliance  must  next  be  provided,  taking  es- 
pecial care  to  arrange  for  the  distribution  of  the  load  on  the 
base  over  a  considerable  area  of  plate  so  that  no  harm  may  be 
done  by  the  reaction  from  the  head.  To  this  end  a  support  of 
heavy  timbers  is  usually  the  most  convenient  to  arrange.  These 
various  appliances  being  in  readiness  the  bulged  plate  is  heated 
to  a  low  red,  the  former-block  and  jack  are  adjusted  in  position, 
and  the  plate  is  carefully  forced  back  into  shape.  Several  ap- 
plications of  the  heat  and  of  the  jack  may  become  necessary 
before  the  plate  is  restored  to  its  original  form. 

It  is  thought  by  many  that  the  partial  heating  of  a  steel 
plate  in  this  way  with  no  later  opportunity  for  general  annealing 
is  liable  to  injure  its  homogeneity  and  toughness,  especially  if 
the  operations  are  carried  on  at  too  low  a  temperature,  or  ap- 
proaching what  is  known  as  blue  heat.  This  was  undoubtedly 
true  for  much  of  the  earlier  products  of  the  steel  makers,  and 
there  is  no  doubt  that  the  homogeneity  of  the  metal  is  thus 
somewhat  disturbed.  With  the  latest  and  best  grades  of  boiler 
plate,  however,  little  danger  as  regards  strength  at  least,  need 
be  feared  on  this  score,  and  but  little  hesitation  is  now  felt  in 
reducing  to  shape  a  bulge  of  moderate  depth. 


OPERATION,  MANAGEMENT  AND  REPAIR.  341 

[n]  Split  in  Feed-Pipe. 

A  small  split  in  the  feed-pipe  may  sometimes  be  temporarily 
repaired  by  wrapping  with  heavy  canvas  and  marline,  or  copper 
wire,  it  is,  however,  difficult  to  make  a  tight  joint  with  hand 
wrapping,  especially  with  modern  high  pressures,  and  a  more 
effective  plan  is  to  form  up  a  patch  of  sheet  copper  and  secure 
it  in  place  by  bolted  strap  clamps,  with  a  sheet  of  good  elastic 
packing,  or  a  thin  layer  of  stiff  putty  between  the  patch  and  the 
pipe  to  make  the  joint. 

A  small  hole  in  the  feed-pipe  may,  if  the  metal  is  thick 
enough,  be  stopped  by  drilling  and  tapping  out  and  riveting 
in  a  small  screw  plug.  Soft  solder  when  applied  with  skill  may 
also  be  used  to  stop  pin-holes,  or  to  aid  in  securing  a  suitable 
plug  in  a  larger  hole.  If,  however,  the  hole  is  of  any  consider- 
able size,  or  if  the  metal  is  thin  about  its  edges,  some  form  of 
patch,  as  described  above,  must  be  made  use  of. 

All  such  repairs  are,  of  course,  only  temporary,  and  at  the 
earliest  convenient  opportunity  the  damaged  length  of  pipe 
should  be  replaced  with  new. 

In  some  cases  with  copper  pipes,  however,  where  the  neces- 
sary materials  and  skill  are  available,  it  may  be  desired  to  under- 
take a  more  permanent  repair  by  brazing  a  patch  over  the  hole 
or  split.  To  this  end  the  metal  about  the  defective  spot  is  first 
cleaned  with  file,  emery  cloth  and  acid.  The  patch  similarly 
cleaned  is  cut  from  sheet  copper  of  about  the  same  thickness 
as  that  of  the  pipe,  formed  to  fit  over  the  defective  spot  and 
wired  in  place.  A  clear  coke  or  charcoal  fire  is  then  prepared 
on  a  forge  and  the  pipe  placed  in  position.  The  spelter  or  hard 
solder,  mixed  with  borax  as  the  flux,  is  then  placed  in  position 
on  the  inside  of  the  pipe  and  the  whole  carefully  heated.  At 
the  proper  temperature  the  spelter  will  melt  and  run  in  between 
the  patch  and  pipe,  thus  forming  a  joint  between  the  two.  Care 
must  be  exercised  in  this  operation  in  order  to  avoid  danger  of 
overheating  or  "burning"  the  copper.  The  resulting  loss  of 
strength  has  been  referred  to  in  Section  3. 

Sec.  43.    ENGINE  OVERHAULING,  ADJUSTMENT 
AND  REPAIRS. 

We  shall  undertake  in  this  section  only  a  few  hints  regard- 
ing the  more  common  operations  involved  in  the  overhauling, 
adjustment  and  repair  of  marine  machinery. 


342  PRACTICAL  MARINE  ENGINEERING. 

[i]   Cylinders. 

First,  in  the  main  engine,  the  cylinder  covers  must  be  re- 
moved at  proper  intervals,  and  attention  given  to  the  condition 
of  the  wearing  surfaces  and  of  the  piston  springs.  The  troubles 
most  liable  to  be  found  are  cutting  and  scoring  of  these  sur- 
faces, and  derangement  or  breakage  of  the  springs.  The  nuts  of 
the  follower  studs  and  all  other  forms  of  screwed  fastenings 
should  also  be  examined,  in  order  that  any  tendency  toward 
loosening  up  or  backing  off  may  be  noted  and  checked. 

To  examine  the  condition  of  the  piston  the  follower  plate 
is  lifted  and  the  springs  and  packing  rings  removed.  The  latter, 
if  wearing  properly,  will  be  of  uniform  thickness  around  the  en- 
tire circumference,  and  of  uniform  polish  on  the  outer  surface. 
If  the  piston-rod  is  bent  or  cylinder  bore  not  quite  in  line  with 
the  motion  of  the  rod,  the  ring  will  wear  wedge-shaped  in  cross 
section.  In  replacing,  care  should  be  taken  to  note  the  degree 
of  tightness  of  the  ring  when  set  out  with  its  springs.  This 
should  be  such  as  to  support  the  ring  anywhere  along  the  bore, 
but  not  so  much  that  the  ring  cannot  be  pushed  along  by  hand, 
using  moderate  force.  In  closing  up  the  cylinder  or  valve-chests, 
especial  care  should  be  taken  to  see  that  all  nuts,  split  pins,  etc., 
are  properly  secured  in  place,  and  that  no  tools,  waste  or  other 
foreign  substance  are  left  within.  Neglect  of  this  latter  point 
has  often  been  the  cause  of  serious  trouble,  resulting  in 
broken  cylinder-heads,  bent  piston-rods,  broken  valves,  port 
metal,  etc. 

To  test  the  tightness  of  the  joints  of  the  cylinder  liners,  the 
cylinder  being  open,  steam  is  admitted  to  the  jacket  and  the 
joints  are  carefully  examined  top  and  bottom.  Where  there  is 
no  manhole  on  the  lower  head,  as  is  common  with  small  cylin- 
ders, a  leak  of  any  significance  will  become  evident  by  opening 
the  lower  indicator  cock. 

In  order  to  test  the  tightness  of  the  piston  under  steam, 
the  cylinder-head  being  in  place,  we  may  proceed  as  follows : 
Put  the  engine  and  links  in  such  position  that  a  little  steam  can 
be  admitted  on  top  of  the  piston  and  then  open  the  bottom 
indicator  cock.  Then  admit  the  steam,  usually  through  the 
starting  valve,  and  if  it  blows  through  the  lower  cock  the  piston 
is  thus  shown  to  be  leaky.  For  a  thorough  test  it  will  be  well 
to  try  the  leakage  in  both  directions;  that  is,  from  top  to 
bottom,  as  above,  and  similarly,  from  bottom  to  top. 


OPERATION,  MANAGEMENT  ./.YD  REPAIR.  343 

[2]  Pin  Joints  and  Bearings. 

The  various  pin  joints  and  cylindrical  bearings  will  need 
attention  according  to  the  special  circumstances  of  the  case.  The 
manner  in  which  a  joint  or  bearing  has  been  working,  both  as 
to  noise  and  temperature,  will  often  serve  as  a  guide  to  those 
which  the  most  require  attention. 

To  examine  the  crosshead  bearings  the  main  points  of  the 
operation  may  be  outlined  as  follows : 

(1)  The  crosshead  with  piston-rod  and  piston  must  be  se- 
cured near  or  at  the  top  of  the  stroke.    This  is  sometimes  done 
by  inserting  pins  or  bolts  in  the  upper  edge  of  the  slide  through 
the  holes  for  securing  the  slipper,  and  allowing  such  to  project 
over  the  top  of  the  guide.     Or  otherwise  it  may  be  done  by 
shoring  in  such  way  as  may  best  be  suited  to  the  details  of  the 
case  in  hand. 

(2)  The  outer  caps  and  brasses  are  removed. 

(3)  A  wooden  chock  lashed  to  the  connecting  rod  is  fitted 
between  its  upper  end  and  the  guide.  This  will  serve  to  support 
the  upper  end  when  free  from  the  crosshead. 

(4)  The  connecting  rod  sloping  in  such  way  as  will  bring  the 
support  of  its  upper  end  upon  the  chock,  the  turning  engine  is 
used  to  revolve  the  crank  down  until  the  parts  are  sufficiently 
clear  to  admit  of  the  examination  desired. 

To  remove  the  crank-pin  brasses  the  main  points  of  the 
operation  may  be  outlined  as  follows : 

(1)  Starting  with  crank  near  its  lower  position  the  bottom 
cap  is  removed  and  landed  on  a  bed  suitably  prepared  for  it. 

(2)  The  turning  engine  is  then  used  to  carry  the  crank  up 
nearly  or  quite  to  the  top  of  the  stroke,  where  the  crosshead  is 
secured  by  hanging  up  or  shoring  as  described  above. 

(3)  The  upper  brass  is  then  secured  and  the  crank  is  rotated 
down  until  the  parts  are  sufficiently  clear  for  the  purpose  in 
view. 

For  like  examinations  of  other  parts,  similar  means  will 
readily  suggest  themselves. 

For  removing  the  lower  brass  of  the  main  pillow-block 
bearings  where  it  is  in  the  form  of  a  half  cylindrical  shell,  it 
needs  simply  to  be  rotated  out  as  noted  already  in  Sec.  21  [ii]. 
A  method  sometimes  used  for  this  purpose  is  to  clamp  to  the 
crank-arm  a  bar  of  steel  carrying  a  projecting  pin  or  bolt  so 
placed  that  it  will  engage  with  the  top  face  of  the  brass  when 


344  PRACTICAL  MARINE  ENGINEERING. 

rotated  around.  The  upper  cap  and  brass  being  then  removed, 
the  shaft  is  rotated  carefully  by  means  of  the  turning  engine, 
and  in  this  way  the  lower  brass  is  forced  around  and  up  until 
free  from  its  bed. 

Bearings  and  journals  of  this  character  may  simply  require 
readjustment,  or  refitting  and  adjustment  as  well.  When  the 
wear  has  been  considerable,  the  liners  or  chock  pieces  between 
the  brasses  will  need  thinning,  in  order  to  reduce  the  clearance 
between  the  journal  and  the  bearing  to  the  propor  amount.  In 
order  to  measure  the  clearance  under  any  given  adjustment,  a 
piece  of  lead  wire  is  employed,  of  somewhat  greater  diameter 
than  the  clearance  is  to  be.  This  wire  is  placed  on  the  journal 
and  the  cap  is  screwed  down  hard,  thus  compressing  it  between 
the  journal  and  the  brass.  The  cap  is  then  removed,  and  from 
the  resulting  thickness  of  the  wire  the  clearance  at  any  point 
between  the  journal  and  the  brass  may  be  readily  measured. 
Such  an  operation  is  called  taking  a  lead.  Several  leads,  if  de- 
sired, may  be  taken  at  once  from  a  bearing,  and  will  thus  serve 
to  map  out  quite  satisfactorily  the  distribution  of  clearance,  and 
thus  to  show  when  the  proper  adjustment  has  been  made.  The 
proper  amount  of  clearance  in  any  given  case  is  somewhat  a 
matter  of  judgment,  and  will,  of  course,  vary  with  the  size  of  the 
journal.  In  ordinary  cases  it  may  be  made  about  .002  of  the 
diamater. 

If  time  is  limited  the  adjustment  may  be  effected  without 
the  taking  of  leads,  as  follows :  The  chock  pieces  or  liners  are 
taken  out  and  the  nuts  are  tightened  up  till  the  brasses  bear  full 
on  the  journal.  Their  positions  are  then  marked,  and  they  are 
then  backed  off  an  amount  determined  by  judgment  or  ex- 
perience with  the  particular  circumstances  of  the  case,  and  the 
liners  are  stripped  to  fit  this  adjustment.  While  this  method  is 
not  as  satisfactory  as  with  leads,  it  is  much  quicker,  and  with 
experience  good  results  may  be  obtained. 

In  connection  with  the  marking  of  the  nuts  for  such  pur- 
poses it  may  be  recommended  as  a  good  plan  to  mark  per- 
manently with  a  line  and  a  numeral  i,  2,  3,  4,  5,  6,  the  faces  of 
all  the  large  nuts  likely  to  be  used  in  making  adjustments.  An 
adjacent  reference  line  on  the  bolt  or  on  the  metal  of  the  bearing 
caps  will  then  furnish  means  for  making  a  record  of  each  adjust- 
ment, or  if  no  permanent  record  is  desired,  such  me^ns  will 
greatly  facilitate  making  the  adjustment  in  any  given  case. 


OPERATION,  MANAGEMENT  AND  REPAIR.  345 

The  refitting  of  bearings  and  journals  on  shipboard  does 
not  usually  extend  beyond  removing  or  smoothing  rough  spots 
caused  by  overheating  and  scoring.  This  may  be  done  by  filing 
followed  by  "lapping"  with  oil  stone  powder  or  dressing  with  an 
oil  stone.  In  some  cases  emery  is  used,  but  great  care  is  then 
necessary  in  order  to  remove  all  particles,  as  if  allowed  to  re- 
main they  will  give  trouble  by  continued  cutting  and  grinding 
in  the  bearings.  The  brasses  are  similarly  redressed,  usually  by 
scraping.  The  nature  of  the  contact  between  the  brass  and  the 
journal  is  tested  by  lightly  smearing  the  latter  with  red  lead 
and  then  applying  the  brass  in  place  and  lightly  rotating  : 
and  forth.  The  high  spots  will  then  be  shown  by  the  red  lead 
and  may  be  further  dressed  down  till  a  satisfactory  fit  is  obtained. 
It  may  be  noted  that  where  brasses  are  thus  fitted  up  each 
one  may  show  a  satisfactory  fit  when  tried  separately  and  with- 
out external  constraint,  and  yet  when  in  place  they  may  be 
unable  to  come  to  the  same  relative  positions  on  the  journal  and 
make  satisfactory  contact  with  it.  For  this  reason  it  is  prefer- 
able to  test  the  contact  with  the  brasses  together  and  regularly 
secured  in  place.  This  is  not  always  possible,  however,  by  reason 
of  the  additional  time  required,  and  judgment  in  all  such  cases 
must  be  used,  having  in  view  the  various  circumstances  of  the 
case  in  hand. 

[3]  Cross  Head  Guides. 

The  main  guides  and  cross  head  slides  must  receive  atten- 
tion, both  as  regards  cutting  or  uneven  wear,  and  as  regards 
the  question  of  adjustment.  The  result  of  wear  is  to  throw  a 
cross-breaking  stress  on  the  piston-rod  at  each  stroke,  as  the 
cross  head  is  forced  over  by  the  oblique  action  of  the  connecting 
rod  to  a  bearing  on  the  guides.  Care  must  therefore  be  taken 
that  when  the  engine  is  turned  without  a  load,  the  guide  surface 
remains  in  full  contact  with  the  face  of  the  slide,  and  therefore 
in  a  condition  to  support  and  guide  the  lower  end  of  the  piston- 
rod  in  a  path  consistent  with  the  movement  of  the  rod  in  the 
axis  of  the  cylinder.  If  this  condition  is  not  fulfilled  the  neces- 
sary adjustments  must  be  made  in  the  manner  be*t  suited  to' 
the  structural  arrangements  of  the  case  in  hand. 

To  remove  the  slipper  or  bearing  piece  for  examination  or 
refitting,  screw  eyes  may  be  screwed  into  holes  in  its  upper 
edge  made  for  the  purpose,  and  from  these  the  slipper  may  be 
supported  by  means  of  wire  rope  or  stout  wire  wound  around 


346  PRACTICAL  MARINE  ENGINEERING. 

a  bar  suitably  supported  and  secured  above  the  slipper.  The 
bolts  holding  the  slipper  to  the  crosshead  are  then  removed  and 
the  crosshead  forced  over  by  screw  or  hydraulic  jack  or  other 
convenient  means,  sufficient  to  ease  the  pressure  between  the 
slipper  and  the  guide.  The  slipper  may  then  be  lowered  by  using 
the  bar  as  an  axle  and  the  rope  or  wire  will  readily  follow  down 
between  the  crosshead  and  guide  surface. 

[4]  Crosshead  Marks. 

In  connection  with  the  adjustment  of  the  moving  parts  of 
the  engine  it  is  well  to  have  a  mark  on  the  crosshead  and  cor- 
responding marks  on  the  guide,  showing  the  extreme  positions 
of  the  piston  when  in  contact  with  the  cylinder  heads,  top  and 
bottom;  also  two  marks  placed  slightly  within  the  latter  and 
showing  the  ends  of  the  natural  stroke,  and  a  mark  placed  mid- 
way between  the  two  latter,  showing  the  location  of  the  piston 
when  in  midstroke.  The  distance  from  the  extreme  marks  to 
those  showing  the  ends  of  the  stroke,  shows  the  amount  of 
clearance  proper  between  the  piston  and  the  cylinder  heads 
when  the  former  is  at  the  ends  of  the  stroke. 

This  will  vary  with  the  size  of  the  engine  and  character  of 
the  workmanship,  but  it  is  usually  found  between  y±  and  ^  or 
24  inches,  being  a  little  more  at  the  bottom  than  at  the  top,  to 
allow  for  the  general  tendency  of  the  parts  to  lower  rather  than 
to  rise  through  the  effect  of  wear. 

To  determine  these  points  a  convenient  reference  mark  is 
first  placed  on  the  crosshead.  The  connecting  rod  may  then  be 
disconnected  and  the  parts  hoisted  up  as  far  as  they  will  go, 
or  until  there  is  contact  between  piston  and  head.  A  mark  is 
then  made  on  the  guide  corresponding  to  that  on  the  crosshead. 
The  parts  are  then  lowered  down  as  far  as  they  will  go,  or  until 
there  is  contact  between  the  piston  and  the  lower  head,  and 
anothef  mark  is  made  on  the  guide  corresponding  to  that  on 
the  crosshead.  The  distance  between  these  is  then  taken,  and 
from  it  is  subtracted  the  length  of  stroke.  The  remainder  is 
then  divided  between  the  two  clearances,  top  and  bottom. 
Midway  between  the  two  inner  points  a  point  may  be  placed 
to  indicate  the  location  for  mid  or  half  stroke. 

Thus,  if  the  stroke  is  36  inches  and  the  distance  found  as 
above  is  37  inches,  the  I  inch  difference  is  to  be  divided  between 
the  two  clearances,  giving  to  the  upper,  say,  7-16,  and  to  the 


OPERATION,  MANAGEMENT  AND  REPAIR.  34? 

lower  9-16  inch.  These  differences  are  then  laid  off  within  the 
outside  marks,  and  the  points  thus  given  will  serve  at  any  time 
as  a  guide  for  the  adjustment  regarding  clearance  proper,  while 
the  movement  of  the  piston  may  be  readily  brought  to  conform 
to  these  limits  by  suitable  adjustment  of  the  liners  or  chock 
pieces  in  the  joints  and  bearings  of  the  connecting  rod  and 
crank-shaft.  The  36  inches  may  then  be  divided  equally  and 
the  mark  placed  to  show  mid  stroke,  such  a  point  being  some- 
times of  use  in  connection  with  the  setting  of  the  valve. 

Another  method  of  determining  the  clearance  which  is  avail- 
able when  the  cylinders  have  manholes  is  as  follows :  The  man- 
holes are  removed  and  a  number  of  balls  of  stiff  red  lead  or  other 
putty  and  faced  with  plumbago  are  distributed  on  the  top  of  the 
piston  and  on  the  inside  of  the  lower  head.  The  engine  is  then 
given  a  revolution  by  means  of  the  turning  engine  and  the 
balls  are  collected.  This  method  serves  to  show  just  how  the 
clearance  is  distributed,  and  is  therefore  a  valuable  test  for  a 
bent  piston-rod,  a  condition  which  will  throw  the  piston  out  of 
position  and  give  greater  clearance  on  one  side  than  on  the 
other. 

[5]  I/ining  Up. 

An  important  feature,  both  of  the  original  setting  up  of  ma- 
chinery and  of  its  overhauling  and  adjustment,  is  the  determina- 
tion or  correction  of  the  alignment  of  the  various  moving  parts. 
It  is  clear,  of  course,  what  the  condition  of  proper  alignment  is. 
For  a  marine  engine  it  may  be  briefly  stated  as  follows : 

(1)  The  centers  or  axes  of  the  main  pillow  block  bearings 
should  all  be  in  one  straight  line,  which  will  coincide  with  the 
crank-shaft  axis,  and  which  we  will  take  as  a  standard  or  line  of 
reference. 

(2)  The  axes  or  center  lines  of  the  cylinders  should  all  be 
in  the  same  vertical  plane  containing  the  center  line  of  (i),  and 
they  must  also  be  at  right  angles  to  this  line. 

(3)  The  same  vertical  plane  should  also  contain  the  axes  or 
center  lines  of  all  the  crosshead  pins. 

(4)  The  axes  or  center  lines  of  the  crank-pins  or  crank-pin 
bearings  in  the  connecting  rods  must  also  be  parallel  to  the 
center  line  in  (i). 

(fO  The  surfaces  of  the  main  guides  must  be  parallel  to  the 
plane  in  (2). 

(6)  The  line  shaft  must  be  in  line  with  itself,  and  unless  a 


348  PRACTICAL  MARINE  ENGINEERING. 

flexible  coupling  is  provided  between  this  and  the  crank-shaft 
it  must  also  be  in  line  with  the  crank-shaft,  as  determined  by  the 
line  in  (i). 

The  same  general  principles,  of  course,  control  the  align- 
ment of  the  valve  gear  and  the  various  other  moving  parts,  such 
as  the  starting,  handling  and  drain  gear,  attached  pumps,  etc., 
but  into  these  we  need  not  go  in  further  detail. 

The  implements  used  in  establishing  the  relation  between 
these  various  lines  and  planes  will  naturally  vary  with  the  circum- 
stances, but  are  usually  found  among  the  following: 

The  level,  plumb  line  and  square. 

The  straight  edge. 

The  stretched  wire  or  cord. 

Provision  for  using  a  line  of  sight. 

A  straight  line,  such  as  that  for  a  line  of  shafting,  may  be 
determined  by  either  of  the  latter.  The  sag  in  a  piano  wire  of 
known  size  and  length  and  stretched  with  a  known  weight  over 
a  pulley  is  a  matter  which  may  be  found  by  a  computation,  into 
which  we  cannot  enter  here,  or,  better  still,  it  may  be  deter- 
mined in  the  open  air  by  the  aid  of  a  surveying  instrument  with 
the  usual  cross  hairs.  A  table  giving  the  sag  at  various  points 
between  the  ends  for  known  lengths  and  for  a  known  stretching 
weight  will  then  give  a  leady  means  of  establishing  a  straight 
line  on  board  ship,  by  stretching  the  wire  under  the  same  con- 
ditions, and  then  setting  upward  at  the  various  points  the  amount 
of  the  sag.  A  series  of  levels  may  thus  be  found  which  will  give 
a  true,  straight  line  within  the  limit  of  the  error  in  measure- 
ment. 

When  a  line  of  sight  is  used  the  following  method  may  be 
employed :  A  board  is  fitted  to  the  bearings  at  the  extreme  ends 
of  the  line  to  be  run,  a  hole  of  some  considerable  size  being 
made  in  the  board  at  about  the  center.  This  hole  is  then  covered 
with  a  piece  of  thin  sheet  metal  having  a  small  hole,  say,  1-16  to 
%  inch  in  diameter.  These  sheets  of  metal  are  adjusted  by 
measurement  until  the  small  hole,  as  accurately  as  may  be,  is 
brought  to  the  center  of  the  bearing.  Similar  boards  are  then 
prepared  for  the  other  bearings  or  points  at  which  it  is  desired 
to  establish  the  line.  A  light  is  then  placed  at  one  end  beyond 
the  further  hole,  and  the  eye  at  the  other  end.  An  assistant  then 
adjusts  the  intermediate  pieces  of  sheet  metal  until  the  light 
reaches  the  eye  through  the  entire  series  of  holes.  The  centers 


OPERATION,  MANAGEMENT  AND  REPAIR.  349 

of  these  holes  will  then  serve  to  establish  a  series  of  levels  which 
may  be  marked  on  the  pedestals,  bulkheads  or  other  convenient 
points,  and  which  will  serve  to  establish  the  line  as  desired. 

In  lining  up  and  adjusting  the  engine  itself  so  that  the 
various  conditions  (i)-(5)  above  are  fulfilled,  very  much  will 
depend  on  the  accuracy  and  care  with  which  the  various  pans 
have  been  machined  in  the  shops.  The  gaps  in  the  bed  plate, 
which  receive  the  main  bearing  boxes,  should  be  planed  out  so 
that  they  are  all  in  line.  This  is  a  matter  which  may  be  tested 
by  a  straight  edge,  or  by  measurements  from  a  stretched  wire. 
If  the  bottom  brasses  are  then  adjusted,  all  to  the  same  thick- 
ness, they  will  evidently  support  the  crank-shaft  in  line:  This 
may  also  be  further  tested  by  reference  to  a  line  of  levels,  each  of 
which  is  obtained  by  measuring  the  same  distance  upward  from 
the  bottom  of  each  gap,  and  locating  on  the  bed  plate  at  any 
convenient  point  the  level  thus  determined.  This  adjustment, 
it  may  be  noted,  will  bring  the  axis  of  the  crank-shaft  parallel 
with  the  bottom  of  the  gaps. 

Passing  now  to  the  columns,  the  seatings  for  their  feet 
should  have  been  planed  at  the  same  time  as  the  gaps.  This  will 
bring  the  bottom  of  the  feet  in  a  plane  parallel  with  the  bottom 
of  the  gaps,  and  hence  parallel  with  the  axis  of  the  crank-shaft. 
The  columns  and  cylinders  may  now  be  erected  and  temporarily 
secured  in  place.  The  center  line  for  each  set  of  moving  parts 
may  be  next  determined  as  follows :  A  piece  of  board  is  placed 
across  the  top  of  the  cylinder  and  secured  at  each  end  and  ovei 
one  or  more  stud  bolts.  Then,  by  caretul  measurement  or  the 
use  of  a  beam  compass,  the  center  of  the  bore  at  the  top  of  the 
cylinder  is  located  on  the  board.  A  small  hole  is  then  bored 
at  this  point  and  a  fine  wire  is  passed  through  and  attached  to 
a  little  frame,  which  will  allow  a  few  inches  of  the  wire  to  show 
above  the  board.  The  lower  end  of  the  wire  is  then  located  in 
the  crank-shaft  axis  by  suitable  measurement  from  the  faces  of 
the  bed  plate.  The  wire  is  then  stretched  between  the  two 
points,  and  the  adjustment  of  the  upper  end  verified  by  renewed 
measurement.  If  these  parts  come  accurately  to  place  we  shall 
find  that  the  wire  will  be  truly  central  relative  to  the  opening 
left  in  the  lower  head  for  the  stuffing  box,  and  hence  it  may  be 
taken  as  the  true  center  line  for  the  cylinder  as  a  whole.  We 
shall  also  find  the  wire  at  ,-i  constant  distance  from  the  guid^  sur- 
face on  the  column,  thus  proving  the  latter  parallel  to  the  center 


350  PRACTICAL  MARINE^  ENGINEERING. 

line,  as  required  by  (5)  above.  We  shall  also  find  the  wire  at 
right  angles  to  the  crank-shaft  axis,  as  required  by  (2)  above, 
and,  of  course,  in  a  general  way,  at  right  angles  to  the  bed  plate 
transversely. 

Supposing  these  various  conditions  fulfilled  for  each  center 
line  separately,  then  we  must  see  if  they  are  all  in  the  same 
fore  and  aft  plane  as  referred  to  in  (2)  above.  To  examine  this 
point  we  may  try  to  look  the  wires  "out  of  wind,"  as  the  ex- 
pression is,  by  standing  aft  or  forward  and  trying,  by  sighting 
fore  and  aft,  to  bring  all  the  wires  accurately  behind  the  nearest 
one.  If  these  various  conditions,  for  each  wire  separately  and 
for  all  collectively,  are  not  fulfilled,  then  the  necessary  adjust- 
ments must  be  made  until  they  are  brought  into  the  required 
relations,  as  above  specified.  As  a  further  adjustment  to  be 
made  at  this  time,  a  wire  may  be  stretched  fore  and  aft  along  or 
near  the  guide  surfaces,  and  at  the  same  horizontal  distance 
from  each  vertical  center  line.  This  will  serve  to  show  whether 
the  guide  surfaces  stand  in  the  right  direction  fore  and  aft,  and 
hence,  whether  the  plane  of  each  is  parallel  to  the  central  plane 
defined  in  (2)  above. 

In  setting  up  attached  auxiliaries,  such  as  air,  circulating 
or  feed-pumps,  the  principles  used  will  be  similar  to  those  al- 
ready discussed,  while  the  methods  used  will  depend  upon  the 
particular  circumstances  of  the  case.  If  the  seatings  are  located 
on  the  bed  plate  they  will  probably  be  planed  at  the  same  time 
as  the  main  bearing  gaps,  and  if  the  pump  bases  are  faced  at  the 
same  time  they  are  bored,  their  axes  will  come  at  right  angles  to 
the  seatings,  and  hence  parallel  to  the  axes  of  the  main  cylinders, 
and  thus  properly  in  line. 

In  order  to  test  the  line  of  the  crosshead  pins  the  connecting 
rod  may  be  hung  from  the  upper  end  and  allowed  to  swing 
partially  free  at  the  bottom.  Then,  by  turning  the  engine  into 
various  positions  in  the  revolution  and  measuring  the  fore  and 
aft  clearance  between  the  crank  webs  and  the  faces  of  the  lower 
end  of  the  rod  when  thus  relieved  of  constraint,  the  accuracy  of 
the  adjustment  can  be  determined.  This  operation  may  be  car- 
ried out  in  the  following  manner:  Assuming  that  it  is  desired 
to  test  the  adjustment  in  the  case  of  an  engine  completely  set 
tip,  the  cap  on  the  lower  end  of  the  connecting  rod  is  removed 
and  the  cross  head  is  shored  up  in  any  convenient  manner.  The 
engine  is  then  turned  slightly  by  hydraulic  jack  or  turning  en- 


OPERATION,  MANAGEMENT  AND  REPAIR.  351 

gine  in  such  direction  as  to  carry  the  crank-pin  away  from  the 
rod  and  thus  leave  the  latter  free  in  a  fore  and  aft  direction,  so 
far  as  direct  contact  with  the  pin  is  concerned.  Measurements 
are  then  taken,  and  the  engine  is  next  moved  around  so  as  to 
bring"  the  pin  against  its  bearing  again,  and  then  on  to  a  new 
position.  Here  the  crosshead  is  again  shored,  the  pin  backed  off 
measurements  taken  as  before,  and  so  on.  In  this  way  the  piston, 
crosshead  and  connecting  rod  are  carried  around  by  resting  on 
the  crank-pin,  and  then  in  each  position  the  connecting  rod  is 
freed  by  shoring  the  crosshead  and  backing  off  the  crank-pin. 
In  case  the  clearance  between  the  crank-pin  brass  and  the  faces 
of  the  webs  is  too  small  to  allow  a  possible  irregularity  of  move- 
ments to  show  itself,  the  regular  brass  may  be  taken  out  and  a 
dummy  brass  or  wooden  block,  with  sufficient  clearance  for  all 
possible  motion,  may  be  fitted  in  its  place. 

In  locating  a  line  shaft,  a  wire  or  line  of  sight  may  be  used 
in  the  general  manner  above  described.  After  locating  the  center 
of  the  stern  tube  at  the  stern  post,  the  line  is  run  to  the  after 
end  of  the  crank-shaft  or  on  through  to  the  forward  end,  as  may 
be  desired,  such  point  being  located  by  measurement  accord- 
ing to  the  drawings  of  the  ship,  engine  seating  and  bed  plate. 

In  twin  screw  ships  the  centers  at  the  after  struts  are  located 
by  measuring  at  the  proper  height  the  necessary  distance  out- 
ward from  the  center  line  of  the  stern  post,  at  the  same  time 
squaring  from  this  center  line  so  as  to  bring  both  centers  at  the 
same  height  above  the  keel.  The  two  lines  are  then  set  at  the 
forward  end  at  equal  distances  from  the  keel  at  the  proper  height, 
in  accordance  with  the  drawings.  In  most  cases  the  shafts  are 
not  parallel  with  the  keel,  either  in  a  vertical  or  horizontal  direc- 
tion, usually  inclining  outward  from  forward  aft  and  either  up- 
ward or  downward,  according  to  the  size  of  the  ship  and  other 
circumstances  of  the  case. 

In  the  examination  of  the  adjustment  of  machinery  which 
has  been  already  in  operation,  as  in  the  routine  care  of  marine 
engines,  it  is  not  to  be  supposed  that  the  preceding  operations 
in  all  their  details  will  be  necessary.  Judgment  must  be  used, 
having  in  view  the  particular  points  to  be  examined,  and  the 
best  means  of  effecting  such  examination  in  acordance  with  the 
general  principles  above  discussed. 

Thus  the  fairness  of  the  line  shafting  must  be  tested  occa- 
sionally, lest,  as  time  goes  on,  wear  in  the  bearings  or  changes  in 


352  PRACTICAL  MARINE  ENGINEERING. 

the  structure  of  the  ship  may  throw  it  seriously  out  of  line.  For 
this  purpose  the  following  method  may  be  used :  Three  or  more 
laths  or  battens  are  provided  with  a  straight  edge  on  one  side. 
These  are  then  placed  across  the  shaft  on  the  upper  side,  as 
nearly  horizontal  as  judgment  may  indicate,  being  located  at 
successive  points  along  the  line  of  shafting  to  be  examined.  A 
line  of  sight  is  then  taken  along  the  projecting  lower  edges  of 
the  battens  and  by  adjustment  they  are  brought  parallel  to  each 
other.  Then,  if  they  can  all  be  brought  into  one  line  the  shaft 
itself  is  in  line.  If  not,  the  shaft  is  out  of  line  in  the  vertical 
direction,  and,  by  blocking  or  other  similar  adjustment,  until  the 
battens  are  all  brought  into  one  line  the  amount  by  which  the 
shaft  is  out  at  one  point  relative  to  two  others  is  readily  de- 
termined. 

In  a  similar  manner  the  line  in  the  horizontal  direction  may 
be  tested  by  holding  the  battens  vertical  against  the  side  of  the 
shafting.  This  method  presupposes,  of  course,  that  the  shafting 
throughout  the  part  tested  is  all  of  the  same  size. 

Instead  of  placing  the  battens  on  the  shafting  they  may  be 
placed  on  the  couplings  quite  as  well,  supposing,  of  course,  that 
the  latter  are  all  of  the  same  size. 

Another  test  which  is  sometimes  used  consists  in  slacking 
the  coupling  bolts  at  a  coupling  near  which  it  is  suspected  that 
the  shaft  is  not  in  line,  and  noting  whether  there  is  any  tendency 
for  the  two  parts  of  the  coupling  to  open  out  on  one  side  or 
another.  Such  an  opening  out  then  shows  an  unfairness  in  the 
line  in  one  way  or  another,  according  to  the  side  on  which  it 
appears. 

[6]  Valve  Gear. 

In  the  routine  examination  of  the  valve  gear  the  points  to 
be  looked  after  are  wear  and  lost  motion  in  the  excentrics  and 
excentric  straps,  in  the  link  block  brasses  of  the  Stephenson  link, 
or  in  like  parts  of  other  forms  of  valve  gear,  in  the  various  pin 
joints  and  connections,  and  abrasion  or  uneven  wear  in  the 
valve  faces  or  seats.  In  the  case  of  the  excentrics  and  straps  and 
various  pin  joints,  the  wear  may  be  taken  up  by  the  adjustments 
usually  provided  and  in  the  general  manner  already  outlined  for 
other  similar  parts.  Excessive  or  irregular  wear  in  a  flat  slide 
valve  or  seat  may  require  either  resurfacing  or  renewal,  accord- 
ing to  the  circumstances  of  the  case.  With  piston  valves,  es- 
pecially if  not  fitted  with  rings,  excessive  wear  in  either  valve 


OPERATION,  MANAGEMENT  AND  REPAIR.  353 

or  seat  will  mean  a  serious  steam  leak,  and  will  usually  call 
for  new  parts,  either  for  valve  or  seat  or  both. 

[7]  Thrust  Bearings. 

The  most  common  trouble  with  thrust  bearings  is  scoring 
or  irregular  wear  of  the  bearing  surfaces,  or  a  general  wear 
which  may  allow  the  thrust  shaft  to  move  forward  sufficiently 
to  put  a  pronounced  thrust  on  the  line  and  crank-shafts.  This 
will  result  in  heating  and  wear,  and  may  throw  the  crank-shaft 
bearings  out  of  line.  A  little  clearance  is  usually  allowed  in  the 
shaft  couplings  and  in  the  fitting-up  of  the  crank-shaft  and  crank- 
pin  bearings,  so  as  to  insure  freedom  from  end  thrust  for  the 
crank-shaft  as  a  whole.  If  the  wear  at  the  thrust  collars  should 
exceed  this,  then  a  part  of  the  thrust  would  be  transmitted  to 
the  crank-shaft,  with  effects  as  above  noted. 

With  adjustable  or  horse-shoe  collars  this  trouble  is  readily 
adjusted  by  moving  the  collars  back  by  means  of  the  adjusting 
nuts  provided.  With  the  plain  type  of  thrust  bearing  as  in  Fig. 
149  the  bearing  as  a  whole  must  be  moved  slightly  aft  by  means 
of  the  screws  provided  for  the  purpose. 

[8]  Circulating  Pump. 

The  engines  for  operating  such  pumps  require  the  care 
necessary  in  all  machinery  of  such  type,  the  principles  of  which 
have  been  already  discussed.  The  runner  simply  needs  examina- 
tion from  time  to  time  to  make  sure  that  it  is  running  freely, 
but  without  undue  clearance  on  either  side  in  its  casing.  Trouble 
is  often  met  with  in  the  maintenance  of  circulating  pumps  by 
the  choking  of  the  inlet  passage,  valve  or  strainer  by  marine 
growth  of  one  form  or  another.  To  aid  in  freeing  the  strainer 
and  inlet  passage  a  connection  is  often  made  with  the  delivery 
of  one  of  the  fire  or  other  auxiliary  pumps  by  means  of  which 
they  may  often  be  cleared  without  the  need  of  regular  over- 
hauling. 

[9]  Condensers. 

The  chief  troubles  to  be  expected  with  condensers  are  as 
follows : 

(1)  Leakage  about  the  tube  ends  through  the  packings  from 
the  salt  water  to  the  steam  side. 

(2)  Corrosion  and  pitting  of  the  tubes,  resulting  ultimately 
in  the  development  of  holes  or  the  breaking  of  the  tubes  and 
similar  leakage,  as  in  (i). 


354  PRACTICAL  MARINE  ENGINEERING. 

(3)  Fouling  of  the  tubes  with  oil  deposit  on  the  condensing 
surface,  thus  decreasing  the  heat  conductivity  of  the  metal  and 
the  efficiency  of  condensation. 

The  condenser  heads  or  bonnets  must  therefore  be  taken  off 
from  time  to  time  and  the  condition  of  the  tube  ends  and  pack- 
ings examined  with  reference  to  the  matter  of  leakage  and 
general  condition. 

To  test  the  condenser  for  leakage  the  main  inlet  and  out- 
board valves  should  be  tightly  closed,  and  the  connections  to 
the  low  pressure  cylinder  and  air  pump  closed  by  blank  flanges. 
The  condenser  heads  may  then  be  taken  off  and  the  steam  side 
filled  with  water  while  a  watch  is  kept  for  leaks  on  the  tube 
sheets  at  each  end.  It  is  also  desirable  to  be  able  to  put,  by 
means  of  a  hand-pump  or  otherwise,  a  pressure  of  15  or  20 
pounds  per  square  inch  on  the  contained  water,  thus  making 
the  development  of  the  leak  more  certain.  It  is  sometimes 
desirable  to  be  able  to  identify  both  ends  of  the  same  tube.  This 
may  be  readily  done  by  passing  a  wire  through  from  one  end  to 
the  other.  In  some  cases  a  lamp  held  at  one  end  will  serve  the 
same  purpose. 

When  provided  with  bonnets  for  the  purpose,  the  steam 
side  of  the  condenser  must  also  be  occasionally  opened  and  the 
tubes  and  interior  surfaces  examined,  with  reference  to  grease 
coating  and  general  condition.  Where  there  may  be  any  doubt 
as  to  the  condition  of  the  tubes  in  the  interior,  a  few  should  be 
drawn  when  the  heads  or  head  bonnets  are  removed,  and  their 
condition  determined. 

So  far  as  the  accumulation  of  grease  is  concerned,  the  con- 
denser may  be  cleaned  by  the  use  of  hot  soda  or  lye  water,  care 
being  taken  to  wash  it  out  thoroughly  so  as  to  remove  any 
excess  of  the  alkali.  When  soda  is  used  for  the  boilers  it  is  some- 
times introduced  into  the  condenser,  there  entering  the  feed 
water  and  then  passing  on  to  the  boiler.  It  may  be  questioned, 
however,  whether  this  is  the  best  plan,  as  accumulations  of 
grease  only  partly  converted  to  soap  may  thus  be  carried  into  the 
boiler,  there  giving  trouble,  as  already  referred  to  under  that 
head. 

Zinc  plates  are  often  used  on  the  salt  water  side  in  condenser 
heads  to  protect  against  corrosion,  in  a  similar  manner  as  ex- 
plained for  boilers  in  Sec.  40.  The  condition  of  these  plates  and 
of  their  attachment  to  the  shell  should  be  carefully  noted  when 


OPERATION,  MANAGEMENT  AND  REPAIR.  355 

the  condenser  is  opened,  and  such  repairs  made  as  may  be 
required. 

[loj  Air  Pumps. 

The  head,  foot  and  bucket  valves  require  the  most  frequent 
and  careful  examination.  They  often  tend  to  become  coated  by 
an  accumulation  of  a  black,  greasy  paste  formed  from  the  cylin- 
der oil  and  the  material  of  the  wasted  zinc  plates,  if  such  are 
used.  This  accumulation  may  prevent  their  proper  working,  and 
they  should  be  carefully  cleaned  as  occasion  may  offer.  With 
air  pumps  attached  to  the  main  engine,  and  where  the  number  of 
strokes  is  usually  greater  than  with  the  independent  pump,  the 
valves  sometimes  give  trouble  by  severe  pounding  against  their 
seats  and  guards.  This  is  due  to  their  inertia,  and  is  likely  to 
be  more  severe  as  the  valves  are  heavier  and  have  more  litt. 
Light  metal  valves  of  sufficient  number  and  size  to  allow  of 
moderate  lift  are  therefore  to  be  preferred  for  all  such  purposes. 
(See  Figs.  185,  186). 

[n]  Pumps  in  General. 

The  chief  troubles  to  be  expected  in  the  operation  of  the 
various  forms  of  independent  pumps  found  on  shipboard  are 
as  follows : 

(1)  In  the  water  end  the  plunger  rings  or  packing  or  the 
barrel  may  become  worn,  thus  allowing  considerable  leakage  or 
"slip,"  especially  under  high  pressure,  as  in  boiler  feed  pumps. 

(2)  The  water  valves,  either  inflow  or  delivery,  may  become 
worn  or  deranged,  and  thus  fail  to  hold  the  water  as  they  should, 
so  preventing  the  proper  operation  of  the  pump. 

(3)  In  the  steam  end  the  piston  rings  or  cylinder  barrel  may 
be.-ome  worn,  allowing  steam  to  blow  from  one  side  to  the  other 
and  decreasing  the  effective  steam  load  on  the  piston. 

(4)  The  main  steam  valve  or  more  often  some  part  of  the 
auxiliary  steam  operating  gear  may  become  worn  or  deranged 
so  that  the  pump  can  no  longer  properly  operate  under  steam. 

These  various  troubles  must  be  guarded  against  by  periodi- 
cal examination  of  the  points  mentioned  with  a  view  to  wear  or 
derangement  of  any  kind  whatever. 

[12]  Piping. 

Steam  piping  of  copper  if  properly  constrained  may  become 
brittle  and  weakened  in  spots  by  long  continued  expansion  and 
contraction.  An  indication  of  this  mav  often  be  found  in  the 


356  PRACTICAL  MARINE  ENGINEERING. 

wavy  or  irregular  condition  of  the  surface.  Such  pipe  should, 
of  course,  be  replaced  at  the  first  opportunity.  A  repair  may, 
however,  be  made  by  banding  with  screw  clamps  made  of  strap 
iro-i  or  steel  and  closely  spaced  over  the  suspected  part. 

Small  holes  which  may  sometimes  develop  may  be  treated 
with  a  soft  patch  held  in  place  by  a  screw  clamp,  by  filling  with 
solder,  or  by  a  patch  as  in  Sec.  42  [2]  (10),  according  to  the  cir- 
cumstances of  the  case.  Leakage  and  like  trouble  with  steel 
piping  may  be  treated  by  the  same  general  means  as  for  boilers, 
and  as  discussed  in  the  preceding  section. 

Sec.  44-     SPARE  PARTS. 

In  order  to  provide  for  the  results  of  regular  wear,  and  for 
the  possibilities  of  accident  it  is  customary  to  carry  a  certain 
number  of  spare  parts,  especially  of  those  most  likely  to  require 
replacement  either  as  the  result  of  wear  or  accident.  The  pieces 
carried  and  their  number  will  depend  entirely  of  course  on  the 
extent  to  which  it  may  be  necessary  or  desirable  to  fit  out  the 
ship  with  provision  for  such  wear  and  emergency.  No  attempt 
will  therefore  be  made  to  give  any  complete  list  of  such  parts, 
but  among  those  more  commonly  carried  the  following  may  be 
mentioned :  Grate  bars,  bearers  and  dead-plates,  furnace  and  ash- 
pit doors,  boiler  tubes,  manhole  and  handhole  plates  with  fit- 
tings, safety  valve  springs,  boiler  gauge  cocks,  fittings  for  boiler 
water  gauges,  feed  check  valves,  bottom  blow  valve,  surface 
blow  valve,  piston  and  pump  rods  for  the  various  pumps,  valves, 
valve  guards  and  springs  for  the  various  pumps,  follower  bolts, 
nuts  and  springs  for  the  various  steam  pistons,  brasses  for  the 
various  bearings,  horseshoes  for  the  thrust  bearing,  propeller 
blades,  valve  stems,  metallic  packing  for  the  various  stuffing 
"boxes  where  it  is  used,  shaft  coupling  bolts,  emergency  shaft 
coupling,  condenser  tubes  and  glands,  evaporator  and  distiller 
tubes,  evaporator  coils,  one  section  of  crank-shaft,  if  made  in 
sections. 

Sec.  45.    LAYING  UP  MARINE  MACHINERY. 

The  chief  dangers  to  marine  machinery  when  not  in  use  arise 
from  the  likelihood  of  rust  and  corrosion.  Fundamental  prin- 
ciples relating  to  these  chemical  changes  have  been  discussed  in 
Sec.  40,  and  by  reference  to  that  point  it  will  be  seen  that  the 
chief  points  to  be  attended  to  relate  to  the  protection  of  the  sur- 
face from  moisture  and  corroding  acids.  Where  applicable  a 


OPERATION,  MANAGEMENT  AND  REPAIR.  357 

good  metallic  paint  well  laid  on  will  be  found  the  most  efficient 
and  satisfactory.  In  such  case  the  surfaces  must  be  dry  and 
well  cleaned  in  accordance  with  the  principles  discussed  in  Sec.  42 
[i]  (10).  For  finished  surfaces  or  bright  work  generally,  where 
paint  would  not  be  suitable,  a  coating  of  heavy  cylinder  or  other 
like  oil  may  be  used,  or  perhaps  even  more  commonly  a  mixture 
of  white  lead  and  tallow  in  about  equal  proportions.  Either  of 
these  will  efficiently  protect  the  surfaces  and  will  remain  for  a 
long  period  of  time  without  becoming  too  hard  to  admit  of  ready 
removal,  especially  with  the  aid  of  a  little  kerosene  or  other 
light  oil. 

One  of  the  most  important  features  connected  with  the  lay- 
ing up  of  marine  machinery  is  the  getting  rid  of  water  contained 
in  the  various  cylinders,  pipes,  bends,  valve  chambers,  etc.  The 
draining  off  of  the  water  is,  of  course,  of  importance  relative  to 
the  question  of  rust  and  corrosion,  but  it  may  be  of  even  still 
greater  importance  relative  to  the  question  of  freezing  and 
possible  rupture  of  the  chamber,  casing,  or  pipe  containing  the 
water.  Many  a  cracked  cylinder  or  valve  chest  or  globe  valve 
chamber,  or  split  in  pipe  elbow  or  bend,  or  in  boiler  or  condenser 
tube,  etc.,  has  been  due  to  incomplete  drainage  of  water  and 
subsequent  freezing.  In  laying  up  marine  machinery,  therefore, 
where  there  is  any  liability  of  freezing,  a  systematic  study  must 
be  made  of  the  piping  systems,  pockets,  etc.,  where  water  might 
collect  and  by  freezing  result  in  damage.  These  remarks  apply 
especially  to  piping  and  fittings,  to  small  auxiliaries,  to  the  con- 
denser, and  to  water-tube  boilers.  If  the  proper  drains  are  not 
fitted  and  the  water  cannot  be  gotten  out  in  any  other  way,  then 
the  necessary  joints  should  be  broken  and  the  water  removed 
in  this  manner. 


358 


PRACTICAL  MARINE  ENGINEERING. 


CHAPTER  VII. 
VALVES  AND  VALVE  GEARS. 

Sec.  46.     SI/IDB  VAI/7ES. 

[ij  Simple  Slide  Valve. 

In  Fig.  207  VW  represents  a  simple  slide  valve,  supposed 
to  be  surrounded  by  live  steam  in  the  steam  chest  C  C.    P  and  Q 

c 


Fig.  207      Plain  Slide  Valve,  Mid  Position. 


are  the^  ports  leading  to  opposite  ends  of  the  cylinder  as  shown, 
while  E  is  the  exhaust  port  or  passage  leading  to  the  condenser 
or  to  the  air,  as  the  engine  is  condensing  or  non-condensing. 
It  is  the  business  of  the  valve,  as  we  shall  explain  later,  to  move 


Fig.  208.     Plain  Slide  Valve,  Position  for  End  of  Stroke. 

back  and  forth,  thus  alternately  uncovering  the  ports  P  and  Q 
and  admitting  steam  from  the  chest  to  the  ends  of  the  cylinder. 
While  the  steam  is  thus  being  admitted  at  one  end  of  the  cylin- 
der, it  must  be  allowed  to  escape  from  the  other  to  the  exhaust 


VALVES  AND  VALVE  GEARS. 


359 


passage  E,  and  thus  the  piston  is  moved  to  and  fro  in  the  cylin- 
der and  the  operation  of  the  engine  becomes  continuous. 

If  we  suppose  in  Fig. 
207  that  the  valve  is  in  the 
middle  of  its  travel  back 
and  forth,  or  in  mid  posi- 
tion as  it  is  commonly 
called,  then  the  distance 
A  B  by  which  the  edge  of 
the  valve  on  the  steam 
side  extends  over  the 
edge  of  the  port  is  called 
the  steam  lap.  Similarly 
the  distance  CD  by  which 
the  edge  of  the  valve  ex- 
tends over  the  port  on  the 
exhaust  side  is  called  the 
exhaust  lap.  In  Fig.  208 
let  the  piston  be  at  the 
end  of  the  stroke  and  the 
valve  in  the  position 
shown.  Then  the  distance 
A  B  by  which  the  port  is 
uncovered  to  steam  is 
called  the  steam  lead,  while 
the  distance  CD  by  which 
the  other  port  is  uncov- 
ered for  exhaust  is  called 
the  exhaust  lead.  In  gen- 
eral, therefore,  lead  is  the 
amount  by  which  the  valve 
is  open  when  the  piston  is 
at  the  end  of  the  stroke. 
In  Fig.  209  are 
shown  a  series  of  corre- 
sponding positions  for 
valve  and  piston  during  a 
single  stroke  of  the  latter. 
The  position  a  is  the  same 
as  that  of  Fig.  208  and 
the  port  is  open  for  the 


36o  PRACTICAL  MARINE  ENGINEERING. 

.admission  of  steam  on  I  he  left  and  for  exhaust  on  the  right. 
The  piston  is  at  the  end  of  the  stroke  and  just  about  to 
begin  the  stroke  to  the  right.  In  b  the  piston  has  advanced 
about  10  per  cent,  of  the  stroke,  and  the  valve  has  moved  so 
that  the  port  is  nearly  wide  open.  Up  to  this  point  the  piston 
and  valve  have  been  moving  in  the  same  direction.  In  c  the  piston 
has  advanced  to  about  60  per  cent,  of  the  stroke,  while  the  valve 
has  come  back  and  has  just  closed  the  port  to  the  entrance  of 
steam.  This  is  called  the  point  of  cut-off.  Between  b  and  c  the 
piston  has  been  moving  on,  but  the  valve  has  been  moving  back 
in  the  opposite  direction.  In  d  the  piston  has  moved  still  further 
on  while  the  valve  is  still  moving  to  the  left,  and  has  just  reached 
the  point  where  the  exhaust  opening  on  the  right  is  closed.  This 
is  called  the  point  of  exhaust  closure,  and  the  operation  of  com- 
pressing the  steam  in  the  end  of  the  cylinder  from  this  point  to 
the  end  of  the  stroke  is  called  compression  or  cushion.  In  e  the 
piston  is  still  nearer  the  end  of  the  stroke  on  the  right,  while  the 
valve  has  moved  farther  to  the  left,  and  is  just  about  to  open  the 
port  on  the  left  for  exhaust,  thus  allowing  the  escape  of  the  steam 
which  entered  during  the  early  part  of  the  stroke.  In  f  the  piston 
has  nearly  reached  the  end  of  the  stroke.  The  exhaust  opening  on 
the  left  is  open  still  wider,  while  the  port  on  the  right  is  just 
about  to  open  for  steam.  In  g  the  piston  is  at  the  end  of  the 
stroke,  the  valve  has  moved  so  as  to  make  the  steam  and  exhaust 
openings  still  wider,  and  the  return  stroke  is  about  to  begin. 
This  completes  the  history  of  the  stroke,  and  the  next  or  return 
stroke  follows  after  it  with  like  series  of  events,  and  so  on  con- 
tinuously. 

[2]  Double  Ported  Slide  Valve. 

The  valve  shown  in  the  above  diagrams  is  called  single  ported 
because  it  covers  but  one  set  of  ports  or  openings.  A  double  ported. 
valve  is  shown  in  Fig.  210.  This  is  a  form  of  valve  within  a  valve. 
Thus  taking  one  end  of  the  valve  we  have  at  AB  one  set  of  edges 
respectively  for  steam  and  exhaust,  and  at  A!  Bj  another  like  set. 
Steam  surrounds  the  outside  of  the  valve  and  is  therefore  ready 
to  enter  the  port  P  past  the  edge  A  when  the  valve  moves  suffi- 
ciently to  the  left.  Steam  likewise  enters  freely  at  the  side  into 
the  passage  S,  and  is  therefore  ready  to  enter  the  port  Pl  past 
the  edge  AJt  as  the  valve  moves  to  the  left.  Similarly  as  the 
valve  moves  to  the  right  the  ports  P  and  P!  are  open  to  exhaust 
past  the  edges  B  and  B1?  respectively.  The  passage  Et  leads 


VALVES  AND  VALVE  GEARS. 


361 


over  the  transverse  passage  S,  and  thus  the  entire  exhaust  finds 
its  way  into  E  the  outlet  passage. 

With  a  double  ported  valve  the  area  of  the  port  opening 
required  may  be  obtained  with  a  travel  of  valve  only  one-half  that 
for  a  single  ported  valve,  or  with  the  same  valve  travel,  twice 
the  area  of  port  opening  may  be  obtained.  It  is  this  feature 
which  often  leads  to  the  use  of  a  double  ported  valve  where  it 
is  desired  to  obtain  a  relatively  large  opening  with  small  travel 
of  valve. 

[3]  Piston  Valve. 

The  face  of  the  valves  in  the  types  so  far  noted  is  a  plane,  or 
in  other  words,  they  are  flat  slide  valves.  If  now  we  can  imagine 
such  a  valve  wrapped  up  so  as  to  form  a  cylinder  with  the  valve 


?B 

LONGITUDINAL   SECTION. 


CROSS   SECTION   AND   END   VTEW. 
Fig.  210.     Double  Ported  Valve. 

stem  for  axis,  we  shall  have  a  cylindrical  or  piston  valve  as  shown 
in  Figs.  211,  214,  215.  This  consists  essentially  of  two  heads 
connected  by  an  intermediate  body,  as  shown.  The  steam  enters 
past  the  outside  edges,  for  example,  and  exhausts  past  the  inside 
edges  to  the  exhaust  passage,  in  a  manner  entirely  similar  to 
that  for  the  plain  slide  valve  as  above  described.  Otherwise  the 
steam  may  enter  past  the  inside  edges  and  exhaust  past  the  out- 
side as  described  below  for  the  inside  valve.  The  steam  port  and 
passage  consists  of  an  annular  channel  surrounding  the  valve  and 
connecting  with  a  passage  leading  to  the  end  of  the  cylinder  in 
the  manner  shown.  The  valve  is  placed  somewhat  out  of  center 
with  reference  to  this  annular  passage,  so  that  it  is  quite  shallow 
on  the  side  opposite  the  cylinder,  and  gradually  increases  in 
depth  toward  the  side  nearest  the  cylinder.  This  arrangement, 


362 


PRACTICAL  MARINE  ENGINEERING. 


which  is  shown  in  Fig.  212,  gives  a  cross-sectional  area  of  pas- 
sage varying  in  proportion  to  the  amount  of  steam  flowing 
through  it,  as  may  be  seen  by  noting  in  the  figure  the  natural 
direction  of  flow  of  the  steam,  radially  outward  through  the 


Marine  Engineering' 


\£> 


Fig  211.    Piston  Valve. 


port   opening,    and   then   curving  around   to   flow   toward   the 
cylinder. 

Comparing  the  two  forms  of  valve  it  is  readily  seen  that  in 
the  piston  valve  the  outer  circumference  represents  the  active 


VALVES  AND  VALVE  GEARS. 


363 


part  of  the  valve,  and  corresponds  to  the  plate  AB  of  the  flat 
slide,  as  shown  in  Fig.  210. 

The  great  advantage  of  the  piston  valve  lies  in  the  fact  that 
it  is  perfectly  balanced  as  regards  the  steam  pressures  which 
act  upon  it.  It  is  readily  seen  that  the  flat  slide  valve  is  forced 
against  its  seat  by  the  excess  of  the  pressure  on  its  back  over 
that  on  its  face,  which  excess  will  in  the  usual  case  be  large, 
and  will  give  rise  to  a  heavy  frictional  load  to  be  overcome  by  the 
excentric  acting  through  the  valve  stem.  The  piston  valve,  on 
the  contrary,  is  forced  equally  in  all  directions,  and  hence  moves 


Fig.  212.     Section  Through  Valve  Chest  and   Cylinder. 

freely  so  far  as  the  steam  forces  are  concerned,  and  with  only 
such  frictional  resistance  as  may  be  necessary  to  insure  tight- 
ness against  steam  leaks. 

In  order  to  keep  the  heads  of  the  valve  steam  tight  they 
have  been  very  commonly  provided  with  one  or  more  packing 
rings  of  similar  character  to  those  used  on  the  main  piston,  but 
usually  without  auxiliary  steel  springs  to  force  them  outward. 
Such  an  arrangement  is  shown  in  Fig.  215.  In  the  latest  prac- 
tice, however,  especially  for  quick-moving  engines,  the  special 
rings  are  very  commonly  omitted  entirely,  dependence  being 


364  PRACTICAL  MARINE  ENGINEERING. 

placed  on  a  good  working  fit  at  the  start  and  on  the  rapid  re- 
versals of  motion,  to  reduce  the  leakage  to  a  negligible  amount. 
Such  arrangements  are  shown  in  Figs.  211  and  214.  In  the  latter 
a  solid  working  ring  is  fitted  as  shown,  in  such  manner  that  it 
may  be  readily  removed  and  replaced  with  a  new  one  as  occasion 
may  require. 

The  valve  seat  is  usually  a  separate  piece  of  hard  and  fine 
grained  cast-iron,  fitted  as  shown  in  Fig.  211.  The  ports  in  this 
seat  instead  of  being  continuous  all  around,  thus  dividing  the  seat 
into  separate  parts,  are  usually  bridged  over  at  several  points 
distributed  about  the  circle.  The  head  of  the  valve  is  thus  car- 
ried across  from  one  side  to  the  other,  and  is  prevented  from 
catching  or  jamming,  as  would  very  likely  occur  without  such 
bridging.  Where  valve  packing  rings  are  used  it  is  especially 
necessary  to  provide  such  bridging  in  order  to  prevent  the  ring 
from  springing  out  into  the  port  opening,  and  thus  jamming  the 
valve,  or  causing  other  damage.  In  Fig.  213  is  seen  the  de- 
velopment or  lay-out  of  the  port  for  the  valve  shown  in  Fig.  215. 


J/ai*in<  Engineering 

Fig.  213.     Development  of  Piston  Valve  Port. 

The  bridges  are  placed  on  the  slant  so  as  to  distribute  as  much 
as  possible  the  wear  on  the  valve  rings. 

In  the  case  of  wear  on  the  valve  seat  or  rings,  they  may  be 
replaced  with  new.  When  rings  are  not  used  the  wear  is 
usually  less  rapid,  thus  furnishing  a  further  reason  for  their 
omission.  The  valve  itself,  however,  will  slowly  wear,  and  as 
necessity  may  require  a  new  head  or  new  valve  entire  may  be 
fitted. 

In  some  cases  where  a  piston  valve  takes  steam  on  the  out- 
side, it  is  desired  to  lead  the  steam  to  the  chest  at  one  end  only, 
and  then  to  pass  it  down  to  the  other  end  through  the  inside  of 
the  valve.  In  such  case  as  shown  in  Fig.  215  the  body  of  the 
valve  is  made  hollow  and  as  large  as  possible,  thus  connecting 
the  steam  chest  at  top  and  bottom  as  desired. 

The  valve  stem  passes  through  the  center  of  the  valve  and 
is  usually  secured  with  nuts  at  top  and  bottom,  as  shown  in  the 
figures.  In  case  the  valve  is  hollow  for  the  passage  of  steam 


VALVES  AND  VALVE  GEARS. 


365 


between  the  two  ends,  the  stem  must  be  carried  in  bosses  sup- 
ported by  radial  arms  connected  with  the  valve  heads,  and  as 
small  as  possible  in  order  to  present  the  least  resistance  to  the 
flow  in  either  direction. 


Figs.  214,  215.     Piston  Valves. 

[4]  Equilibrium  Piston. 

The  work  of  moving  the  valve  up  and  down  which  is  thrown 
on  the  excentric  may  be  much  decreased  by  fitting  an  equilibrium 
piston  as  shown  in  Fig.  215  The  cylinder  in  which  this  is  fitted 
is  open  at  the  bottom  to  the  valve  chest,  and  hence  the  full 


366 


PRACTICAL  MARINE  ENGINEERING. 


pressure  of  the  chest  acts  constantly  on  the  lower  side  of  the 
piston.  This  may  be  so  proportioned  as  to  carry  practically 
about  all  the  direct  weight  of  the  valve,  which  thus  floats  on  the 
steam,  requiring  comparatively  small  effort  on  the  part  of  the 
excentric.  to  move  it  back  and  forth. 


Fig.  216.     Joy  Assistant  Cylinder. 

[5]  Joy's  Assistant  Cylinder. 

A  further  development  of  the  equilibrium  piston  is  found  in 
Joy's  assistant  cylinder,  as  shown  in  Fig.  216.  The  purpose  of 
this  fitting  is  to  more  perfectly  carry  the  weight  of  the  valve  uric! 
relieve  the  excentric  and  valve  gear  of  the  work  required  to 


VALVES  AND  VALVE  GEARS. 


367 


move  the  valve.  The  cylinder  is  provided  with  steam  and  ex- 
haust ports,  and  in  fact  with  its  piston  forms  a  small  steam  en- 
gine. The  form  of  the  piston  as  shown  is  such  that  it  forms  its 
own  valve,  thus  simplifying  the  number  of  parts  required.  Power 
for  assisting  the  main  valve  gear  is  thus  obtained  by  the  ad- 
mission of  live  steam  to  the  assistant  cylinder,  and  the  ports  are 
so  arranged  that  cushioning  at  the  ends  of  the  stroke  in  this 
cylinder  absorbs  the  forces  due  to  inertia.  An  important  ad- 
vantage claimed  for  such  types  of  assistant  cylinder  over  the 
ordinary  equilibrium  piston  as  in  Fig.  215  is  a  considerable  de- 
crease in  weight,  the  greater  efficiency  of  the  apparatus  for  the 
purpose  in  view  allowing  of  the  use  of  smaller  sizes. 

Such  forms  of  equilibrium  piston  may,  of  course,  be  fitted 
to  advantage  with  either  the  flat  slide  or  piston  forms  of  valve. 

[6]  Equilibrium  Rings. 

With  a  flat  slide  valve  as  in  Fig.  210  the  full  steam  chest 
pressure  acts  constantly  on  the  back  of  the  valve,  while  a  much 
decreased  pressure  will  act  on  a  part  only  of  the  other  side.  In 


Fig.  211.     Section  Through  Equilibrium  Ring. 

consequence,  the  valve  is  forced  with  strong  pressure  against 
the  seat  and  the  frictional  force  thus  developed  must  be  over- 
come by  the  excentric.  (See  Sec.  73).  With  large  valves  and 
where  the  lubrication  is  scanty  this  may  become  excessive, 


36S  PRACTICAL  MARINE  ENGINEERING. 

causing  the  valve  and  seat  to  cut,  and  throwing  a  great  deal 
of  unnecessary  work  on  the  excentric.  To  relieve  this  condition, 
equilibrium  or  balance  rings  are  often  fitted  on  the  back  of  the 
valve.  Such  an  arrangement  is  shown  in  Fig.  217.  The  inner 
face  of  the  valve  chest  carries  a  ring  of  metal  within  which  is 
cut  a  groove  as  shown.  Within  this  groove  is  a  ring  which  is 
forced  against  the  back  of  the  valve  by  springs  and  screw  ad- 
justment as  shown.  The  back  of  the  valve  is  faced  off  and  thus 
a  joint  is  made  between  the  two,  while  the  space  within  the  ring 
and  between  the  back  of  the  valve  and  face  of  the  cover  is  shut 
off  from  the  steam  within  the  valve  chest,  and  hence  this  part 
of  the  valve  is  relieved  from  the  pressure  of  the  steam.  In  addi- 
tion to  this,  the  space  is  sometimes  connected  by  piping  to  the 
steam  side  of  the  condenser,  thus  bringing  on  this  part  of  the 
back  of  the  valve  only  the  pressure  in  the  condenser.  In  this 
way  the  load  on  the  back  of  the  valve  and  the  resultant 
load  on  the  excentric  may  be  much  decreased,  and  the  opera- 
tion of  the  valves  will  be  correspondingly  smoother,  and 
less  work  will  be  thrown  on  the  excentrics  and  valve  gear  in 
general. 

There  are  several  methods  varying  in  detail  for  the  fitting  of 
the  ring  in  such  an  arrangement,  and  in  the  formation  of  the 
joint  between  the  ring  and  valve  chest  cover,  but  the  principle 
is  the  same  in  all,  and  is  sufficiently  illustrated  by  the  arrange- 
ment of  Fig.  217. 

[7]  Outside  and  Inside  Valves. 

In  the  preceding  figures  for  valves  the  steam  enters  past 
the  outside  edges  and  exhausts  past  the  inside  edges.  Such  is 
known  as  an  outside  valve.  In  some  cases,  However,  it  is  con- 


Fig.  218.     Inside  Valve. 

venient  to  have  this  relation  reversed,  and  to  take  steam  past 
the  inside  edges,  and  exhaust  past  the  outside  edges.  Such  a 
valve  is  shown  in  Fig.  218,  and  is  known  as  an  inside  valve. 

Live  steam  fills  the  space  A  and  enters  the  port  P  past  the 


VALVES  AND   VALVE  GEARS.  369 

edge  C,  while  exhaust  occurs  past  the  edge  F.  The  valve  as  here 
shown  is  in  midposition  and  therefore  C  D  is  the  steam  lap  and 
E  F  the  exhaust  lap.  The  only  difference  in  the  two  forms  of 
valve  is  in  the  relative  amounts  of  outside  and  inside  lap.  In  each 
case,  for  reasons  which  will  appear  later,  it  is  seen  that  the  steam 
lap  is  greater  than  the  exhaust,  being  in  one  case  on  the  outside 
and  in  the  other  case  on  the  inside.  It  is  also  clear  that  the 
outside  valve  moves  with  the  piston  at  the  beginning  of  the 
stroke,  and  opposite  to  it  during  the  latter  part,  while  with  an 
inside  valve  it  moves  opposite  to  the  piston  at  the  beginning, 
and  with  it  during  the  latter  part  of  the  stroke. 

Sec.  47.   MOTION  DUE  TO  SIMPLE  EXCENTRIC  AND  ITS 
REPRESENTATION  BY  VAI,VE  DIAGRAMS. 

[i]  Simple  Excentric. 

We  must  now  inquire  by  what  means  the  valve  can  be 
given  the  motion  necessary  for  the  proper  distribution  of  the 
steam  as  above  described.  The  simplest  of  such  means  is  the 
plain  excentric  as  shown  in  Fig.  219.  This  consists  of  a  cir- 
cular disc  with  center  A  set  on  the  shaft  excentric  or  out  of  the 
center.  The  distance  between  the  two  centers  is  seen  to  be  OA. 
This  is  called  the  eccentricity  or  throw  of  the  excentric."  About 
the  excentric  is  a  strap  ST,  and  attached  to  this  is  a  rod  RR. 


•db 


Fig.  219.     Plain  Excentric,  Skeleton  of  Motion. 

As  the  shaft  turns,  the  excentric  turns  with  it,  and  thus  gives 
to  the  rod  a  to  and  fro  movement  exactly  as  though  it  were  a 
connecting  rod  attached  to  a  crank  OA.  This  principle  of  the 
equivalence  between  an  excentric  and  a  crank  of  equal  throw 
is  very  important,  and  the  motion  should  be  studied  until  it  is 
quite  clear  that  the  operation  of  an  excentric  is  exactly  the  same 
as  that  of  a  small  crank  of  throw  equal  to  that  of  the  excentric.  or 
to  the  distance  from  the  center  of  the  excentric  to  the  center  of 

*Some  writers  understand  by  tlie  term  throw  *  twice  the  above  distance. 
In  the  present  work  we  understand  the  term  to  refer  to  the  distance  OA  as 
stated. 


37o  PRACTICAL  MARINE  ENGINEERING, 

the  shaft.     For  purposes  of  illustration  therefore  we  may  rep- 
resent the  excentric  by  a  crank  of  equal  throw. 

With  this  understanding  let  us  again  examine  Fig.  209,  on 
the  left,  when  it  is  readily  seen  that  the  series  of  movements  de- 
sired is  exactly  such  as  would  be  given  by  a  small  crank  located  at 
an  angle  somewhat  more  than  90  degrees  ahead  of  the  main 
crank.  Or,  in  other  words,  with  the  valve  stem  attached  to 
such  a  small  crank  or  excentric,  the  valve  will  be  so  moved'  that 
the  piston  will  be  forced  to  and  fro  in  the  manner  described  in 
Sec.  46  [i],  and  the  main  crank  will  follow  the  motion  of  the 
excentric.  This  is  what  is  meant  by  saying  that  with  a  slide 
valve  connected  as  in  the  diagrams,  the  excentric  leads  the  crank. 

In  regard  to  the  angle  between  the  crank  and  excentric  it 
is  clear  from  the  diagram  of  Figs.  207,  209,  that  starting  with 
the  valve  in  mid  position,  it  must  move  a  distance  equal  to  the 
lap  before  the  port  will  begin  to  open.  Hence  when  the  piston 
is  at  the  end  of  the  stroke  the  valve  must  already  have  moved 
from  its  mid  position  by  an  amount  equal  to  the  lap  plus  the  lead. 
Suppose  now  that  the  excentric  is  loose  on  the  shaft  and  may  be 
adjusted  as  desired.  In  Fig.  220  let  C  denote  the  crank  on  the 
center.  Then  suppose  the  excentric  first  located  90°  ahead  of  O  C 
as  shown  at  O  A,  where  O  A=O  B=  excentric  throw.  Then  neg- 
lecting the  slight  effect  due  to  the  obliquity  of  the  excentric  rod, 
the  valve  will  be  in  its  mid  position,  as  shown  in  Fig.  207.  Next, 
move  the  excentric  ahead  until  the  valve  has  moved  a  distance 
equal  to  the  lap  plus  the  lead  as  in  Figs.  208,  220.  This  gives  the 
final  location  of  the  excentric  for  the  proper  operation  of  the 
valve,  as  already  described.  The  angle  AOB  through  which  it  is 
thus  necessary  to  move  the  excentric  in  order  to  affect  this  move- 
ment of  the  valve  from  its  mid  position,  or  more  exactly  the  angle 
between  the  excentric  and  the  line  at  right  angles  with  the  crank 
we  shall  term  the  angular  advance.  This  term  is  sometimes  used 
in  reference  to  the  entire  angle  between  crank  and  excentric,  but 
we  shall  prefer  to  understand  by  the  term  the  angle  as  defined 
above.  The  angular  advance  is  usually  denoted  by  the  letter  tf. 
With  the  arrangement  of  gear  shown  in  Fig.  220  the  angle  be- 
tween crank  and  excentric  will  therefore  be  90°+^ 

In  regard  to  the  direction  of  motion  of  the  crank,  it  is  clear 
that  when  the  piston  is  at  the  end  of  the  stroke  and  the  crank  on 
the  center,  the  latter  must  start  off  in  such  direction  as  will  in- 
crease rather  than  decrease  the  opening  of  the  port  for  steam. 


VALVES  AND  VALVE  GEARS. 


37i 


IfJ  the  connections  and  arrangements  of  a  valve  gear  are  known 
no  matter  how  complicated,  this  principle  will  always  furnish  an 
answer  to  the  question  as  to  the  direction  in  which  the  engine  will 
turn.  Thus  in  the  direct  connected  gear,  as  in  Fig.  220,  with  the 
piston  at  the  end  of  the  stroke,  the  crank  moves  in  the  same  di- 
rection as  the  excentric,  or  follows  it,  simply  because  that  is  the 
direction  which  opens  the  port  still  wider  for  steam  admission. 


Fig.  220.     Diagram  Showing  Connections  for  Simple  Valve  Gear. 

With  an  inside  valve  the  excentric  is  set  180°  behind  or  directly 
opposite  the  position  for  an  outside  valve,  as  shown  in  Fig.  221, 
or  at  OBj,  Fig".  220.  In  such  case  the  angle  between  the  crank 
and  excentric  is  90° — d  or  the  angle  $  is  set  off  toward  the  crank 
from  the  90°  position.  It  is  readily  seen  that  this  will  bring  the 
valve  slightly  open  when  the  piston  is  at  the  end  of  the  stroke, 
and  that  the  crank  will  move  leading  the  excentric  because  this  is 


Fig.  221.     Inside  Valve  and  Location  of  Excentric. 


the  direction  which  opens  the  port  wider  for  steam  admission.  It 
is  also  seen  that  to  fulfil  the  same  purpose  the  piston  and  valve 
at  the  end  of  the  stroke  must  move  in  opposite  directions. 

In  some  cases  the  valve-rod  instead  of  being  directly  con- 
nected to  the  excentric  rod  is  worked  through  a  rocker-arm, 
which  reverses  the  motion  as  compared  with  the  direct  connected 
gear.  See  Fig.  222.  This  provides  a  second  mode  of  variation 


372 


PRACTICAL  MARINE  ENGINEERING. 


VACVE    STEM 


Marine  Engin.ef.nnj 


Fig.  222.     Diagram  for  Valve  Connections  Through  a  Rocker  Arm. 

which  may  affect  the  arrangement  of  a  valve  gear,  giving  in  all 
four  combinations,  as  shown  in  the  following  table  : — 


Valve.      Connection. 


Outside 
Inside 
Outside 
Inside 


Direct 
Direct 
Rocker 
Rocker 


Angle  Between  Crank 
and  Excentric. 
90  +  A 
90  —  c 
90  —  (J 
90  -f  6 


Which  Leads. 

Excentric  Leads 
Crank  Leads 
Crank  Leads 
Excentric  Leads 


[a]  Oval  Valve  Diagram. 

We  will  now  proceed  to  an  examination  of  the  effects  due 
to  varying  the  steam  and  exhaust  laps,  and  the  angle  of  advance 
[i].  This  may  be  done  most  conveniently  by  the  aid  of  a  dia- 
gram. In  Fig.  223  let  AB  represent  to  any  convenient  scale  the 
path  of  the  piston.  Then  from  the  various  points  of  AB  corre- 
sponding to  a  series  of  successive  piston  positions,  let  the  dis- 
tance of  the  valve  above  or  below  its  mid  position  be  laid  off,  and 
the  points  thus  found  be  joined  by  a  continuous  line.  For  a 
revolution  or  double  stroke  the  result  will  be  found  somewhat  as 
represented  by  the  curved  line  of  the  diagram.  Thus  at  the 
lower  end  of  the  stroke,  say  at  B,  the  valve  will  be  at  a  distance 
BT  above  mid  position.  When  the  piston  has  gone  on  to  S  it  will 
be  at  a  distance  SJ,at  R  a  distance  RK,  at  P  a  distance  PL,  at 
N  it  will  be  in  mid  position,  and  will  then  pass  below]  and  reach 
a  distance  AV  at  the  end  of  the  stroke  A.  On  the  return  stroke 
the  valve  will  pass  through  a  similar  series  of  locations  deter- 
mined by  the  distances  from  AB  downward  to  the  curve.  With 
this  arrangement  of  diagram  the  movement  of  the  valve  above 
mid  position  is  laid  off  above  the  line  AB  and  vice  versa.  With 
an  outside  valve  this  shows  above  the  line  AB  the  events  for  the 
•///>  stroke  and  below  the  line  the  events  for  the  down  stroke. 


VALVES  AND  VALVE  GEARS. 


373 


With  an  inside  valve  the  relation  is  reversed,  the  events  for  the 
up  stroke  being  shown  below  the  line  and  for  the  down  stroke 
above  the  line. 

We  have  already  seen  that  starting  from  mid  position  the 
valve  must  move  a  distance  equal  to  the  steam  lap  before  the 
port  begins  to  open  for  steam.  Suppose  then,  that  BF  is  laid  off 
equal  to  the  steam  lap  on  the  lower  end  of  the  valve,  and  a  line 
FL  drawn  parallel  to  BA.  Then  it  is  clear  that  the  remaining 
distances  from  FL  upward  to  the  curve  ZTKL  give  the  dis- 


:    /x  s 


Fig.  223.     Oval  Valve  Diagram. 

tances  which  the  edge  of  the  valve  travels  beyond  the  first  edge 
of  the  port,  and  hence  if  the  port  is  sufficiently  wide,  the  actual 
widths  of  port  opening.  At  R  the  farthest  distance  is  reached, 
and  the  edge  of  the  valve  is  at  a  distance  OK  beyond  the  first" 
edge  of  the  port.  It  is  clear  that  the  distance  RK  is  the  throw  of 
the  excentric,  and  that  this  is  equal  to  the  lap  plus  the  greatest 
width  available  for  port  opening.  If  the  width  of  port  is  equal 
to  or  greater  than  OK,  then  the  total  movement  OK  can  be 
utilized  for  opening -and  will  be  its  greatest  value,  while  the  vari- 


374  PRACTICAL  MARINE  ENGINEERING. 

ous  distances  from  FL  to  ZTKGL  will  give  the  entire  history 
of  the  width  of  port  opening  for  corresponding  positions  of  the 
piston.  Very  often,  however,  the  width  of  port  is  less  than  the 
distance  OK.  In  such  case  draw  a  line  IJ  parallel  to  LF  and  at 
a  distance  from  it  equal  to  the  width  of  the  port.  Then  it  is  clear 
that  the  widths  of  port  opening  will  be  given  by  the  distances 
from  FL  to  the  lines  ZTJIL.  Full  opening  is  reached  at  J  or 
with  piston  at  S.  This  continues  to  I,  or  until  the  piston  reaches 
Q.  The  port  closes  at  L  or  when  the  piston  reaches  P.  This  is 
known  as  the  point  of  cut  off  or  steam  closure.  Similarly  the 
port  opens  at  Z  just  before  the  end  of  the  stroke,  and  at  the  end 
is  open  a  distance  FT,  which  therefore  represents  the  steam  lead. 

Having  thus  obtained  a  general  idea  of  the  nature  of  this 
diagram  let  us  examine  by  its  aid  the  effects  of  a  change  in  the 
steam  lap.  This  corresponds  to  raising  or  lowering  the  line 
FL,  and  it  is  readily  seen  that  the  results  of  an  increase,  for  ex- 
ample, are  as  follows :  earlier  cut-off,  steam  opening  nearer  the 
end  of  stroke,  decreased  lead,  decreased  port  opening  all  the  way 
through.  The  results  of  a  decrease  of  lap  are  of  course  in  the 
opposite  direction  respectively. 

In  a  similar  manner  we  may  examine  the  influence  of  a 
change  in  the  exhaust  lap.  This  is  illustrated  in  the  same  figure 
where  M  Y  is  the  lap  line  laid  off  at  a  distance  B  D  from  the 
center  line,  equal  to  the  exhaust  lap  on  the  upper  end  of  the 
valve;  that  is,  on  the  end  which  opens  the  port  to  exhaust  by 
moving  above  the  mid  position.  It  is  thus  seen  that  the  valve 
opens  to  exhaust  at  Y  with  the  piston  a  distance  Y  D  from  the 
end  of  the  stroke,  while  at  the  end  of  the  stroke  it  is  open  a  dis- 
tance D  T  the  exhaust  lead.  Then  during  the  following  stroke 
the  distance  of  the  exhaust  edge  of  the  valve  from  the  corre- 
sponding edge  of  the  port  is  given  by  the  distance  from  D  M  to 
the  curve  T  K  L  M.  At  M  the  port  closes,  and  for  M  C,  the 
remainder  of  the  stroke,  the  steam  undergoes  compression  in  the 
cylinder.  Usually  the  width  of  port  is  somewhat  less  than  the 
total  distance  available,  so  that  the  full  movement  of  the  valve 
cannot  be  utilized  for  actual  opening.  In  such  case  draw  a  line 
G  H  parallel  to  M  Y  and  distant  from  it  an  amount  equal  to  the 
width  of  port.  Then  full  opening  is  reached  at  H  with  piston  at 
W  and  continues  to  G  with  piston  at  U,  the  openings  for  the 
remaining  portions  of  the  stroke  being  given  by  the  distance 
from  M  D  to  Y  T  H  and  G  M. 


VALVES  AND  VALVE  GEARS. 


375 


An  increase  of  exhaust  lap  is  thus  seen  to  produce  the  fol- 
lowing results :  earlier  exhaust  closure  and  longer  compression, 
exhaust  opening  or  release  later  or  nearer  the  end  of  the  stroke, 
decreased  exhaust  lead,  decreased  port  openings  or  decreased 
time  during  which  the  port  is  wide  open.  A  decrease  of  exhaust 
lap  will  of  course,  produce  results  in  the  opposite  direction. 

We  have  thus  far  been  concerned  with  the  influence  of  an 
increase  or  decrease  in  the  steam  or  exhaust  lap.  It  remains  to 
examine  the  influence  due  to  a  change  in  the  angle  3  the  angular 
advance.  If  this  angle  is  increased  and  the  new  series  of  valve 
movements  plotted  as  in  Fig.  223,  it  will  be  found  that  the  oval 
becomes  narrower  and  touches  the  boundary  lines  nearer  the 


Fig.  224.    Oval  Valve  Diagrams. 


corners,  as  shown  in  Fig.  224.  Similarly  with  a  smaller  value  of 
d  the  valve  oval  will  become  wider  or  rounder,  and  will  touch  the 
boundary  lines  farther  from  the  corners,  likewise  in  the  figure  as 
shown.  Remembering  this  and  comparing  Figs.  223  and  224  it 
is  readily  seen  with  the  same  values  of  the  lap  that  changes  in 
the  various  quantities  will  take  place  as  shown  in  the  tabular  ar- 
rangement below.  This  table  shows  at  a  glance  the  variation  in 
the  various  events  due  to  change  in  the  three  items  above  the 
double  line,  as  explained  in  the  foregoing. 


376 


PRACTICAL  MARINE  ENGINEERING. 


Attention  may  also  be  called  at  this  point  to  the  diagram  of 
Pig.  225,  in  which  the  various  quantities  for  an  outside  valve  are 
lettered  and  named  in  position.  A  careful  study  of  this  figure  in 
connection  with  the  valve  positions  of  Fig.  209  will  be  of  great 
aid  in  acquiring  a  good  understanding  of  the  operation  of  a  slide 
valve,  and  of  its  representation  by  means  of  such  a  diagram. 

If  the  measurements  for  the  diagram  are  taken  from  an 
actual  engine  or  from  a  properly  constructed  model,  it  will  be 
found  that  for  the  down  stroke  the  curve  is  more  humped  or 


Angular 
Advance 

Increase 

Decrease 

Steam 
Lap 

Increase 

Decrease 

Exhaust 
Lap 

Increase 

Decrease 

Steam 
Opening 

Earlier 

Later 

Later 

Earlier 

Steam 
Closure 

Earlier 

Later 

Earlier 

Later 

Steam 
Lead 

Increase 

Decrease 

Decrease 

Increase 

Exhaust 
Opening 

Earlier 

Later 

Later 

Earlier 

Exhaust 
Closure 

Earlier 

Later 

Earlier 

Later 

Exhaust 
Lead 

Increase 

Decrease 

Decrease 

Increase 

Greatest 
Port 
Opening 

Same 

Same 

Decrease 

Increase 

rounded  than  for  the  up  stroke,  as  shown  in  the  figures  above. 
That  is,  for  the  same  relative  positions  of  piston  the  valve  will 
be  farther  from  the  center  line  on  the  down  than  on  the  up  stroke. 
This  is  an  effect  due  to  the  angularity  of  the  connecting  rod  of 
the  engine,  and  it  results  that  the  various  points  of  opening  and 
closure,  and  the  values  of  lap,  lead  and  port  opening  cannot  be 
made  the  same  for  both  strokes.  As  is  shown  by  the  diagram 
the  cut-off  is  usually  later  on  the  down  than  on  the  up  stroke, 
and  it  cannot  be  equalized  without  a  serious  derangement  of  the 


VALVES  4ND  VALVE  GEARS. 


377 


other  events.  Instead  of  attempting  to  equalize  any  two  feat- 
ures such  as  steam  lead,  cut-off  or  port-opening,  it  is  usually  bet- 
ter to  so  adjust  the  steam  and  exhaust  laps  above  and  below  that 
the  resulting  combination  of  events  shall  represent  the  best  com- 
promise possible  under  the  circumstances.  If  it  were  not  for  the 
effect  due  to  the  angularity  of  the  connecting  rod,  the  curve 
would  be  an  ellipse,  and  the  distribution  of  the  events  for  both 
strokes  could  be  made  the  same. 


see 


EOT 


EOB 


SOT 


SCT 


S  O  B=Steam  Opening  Bottom. 
E  O  T= Exhaust  Opening  Top. 
E  C  B=Exhaust  Closure  Bottom. 
S  C  T= Steam  Closure  Top. 


.'/urine  Enginttring 

S  C  B= Steam  Closure  Bottom. 
E  C  T= Exhaust  Closure  Top. 
EO  B= Exhaust  Opening  Bottom. 
S  O  T— Steam  Opening  Top. 


Fig.  225.    Oval  Valve  Diagram. 


[3]  Bilgram  Valve  Diagram. 

In  Fig.  226  let  a  circle  be  described  with  OP  as  radius  equal 
to  the  throw  of  the  excentric.  Then  draw  the  radius  OP  at  an 
angle  6  (the  angular  advance)  with  the  horizontal  or  line  AB. 
Then  draw  CD  above  AB  at  a  distance  LM  equal  to  the  lead. 
Then  from  the  point  P  as  center  and  with  PQ  as  radius  describe  a 


378 


PRACTICAL  MARINE  ENGINEERING. 


circle  tangent  to  CD.  Also  on  OP  as  a  diameter  describe  a  circle 
as  shown.  Then  let  A  x  be  any  position  of  the  crank.  Draw  the 
radius  AjO  and  extend  it  back  to  cut  the  circle  on  OP  at  E. 
Then  the  properties  of  this  diagram  are  such  that  the  movement 
of  the  valve  from  mid  position  is  given  by  the  distance  PE,  while 
the  port  opening  will  be  less  than  this  by  PQ  or  PF  the  radius 
of  the  circle  about  P  as  center.  This  radius  equals  the  steam 
lap,  and  the  circle  is  for  that  reason  known  as  the  lap  circle.  It 
follows  that  EF  is  the  port  opening,  or  at  least  the  travel  of  the 
edge  of  the  valve  beyond  the  edge  of  the  port.  The  same  con- 
struction holds  for  all  other  crank  positions,  so  that  we  have  here 
a  means  of  representing  by  straight  lines  and  circles  the  move- 


Fig.  226.    Bilgram  Valve  Diagram. 

ment  of  the  valve,  and  of  thus  determining  the  various  events  of 
the  revolution. 

It  must  be  understood,  however,  that  while  this  construction 
shows  with  fair  accuracy  the  relation  between  the  movement  of 
the  valve  and  of  the  crank,  it  does  not,  without  a  further  special 
construction,  connect  the  movement  of  the  valve  with  that  of  the 
piston.  It  is  the  special  property  of  the  oval  diagram  of  [2]  to 
show  this  latter  relation  for  an  actually  constructed  gear  or  for  a 
model,  where  both  sets  of  measurements  may  be  actually  made. 
It  is  the  special  property  of  the  Bilgram  diagram,  and  others 


VALVES  AND  VALVE  GEARS.  379 

composed  of  straight  lines  and  circles,  to  connect  together  with- 
out actual  measurement  the  movement  of  the  valve  and  crank 
for  the  ideal  case  when  there  is  no  angularity  of  excentric-rod. 
The  error  here  involved  is  usually  small,  and  since  the  diagram 
is  so  easily  constructed,  it  may  be  preferred  for  many  purposes  of 
initial  design. 

It  thus  appears  that  the  distances  of  the  edge  of  the  valve  be- 
yond the  edge  of  the  port  are  given  by  the  intercepts  (shown  by 
the  shaded  part  of  the  diagram  in  Fig.  226),  between  the  two  cir- 
cles, one  on  OP  as  diameter  and  the  other,  the  lap  circle,  about 
P  as  center.  In  case  the  width  of  the  port  is  less  than  the  dis- 
tance G  O,  an  arc  RS  is  drawn  from  P  as  center,  such  that  the 
distance  HS  equals  the  width  of  port.  The  widths  of  opening 
are  then  given  by  the  intercepts  between  J  K  S  R  L  and  the  lap 
circle  with  P  as  center.  It  is  seen  that  the  port  opens  for  steam 
at  J  with  crank  at  A2  and  closes  at  L  with  crank  at  A3,  while 
full  opening  holds  from  S  to  R. 

An  entirely  similar  construction  throughout  with  the  ex- 
haust lap  circle  as  shown  by  the  small  circle  about  P  will  give  the 
various  features  of  the  movement  on  the  exhaust  side. 

The  results  of  a  change  in  the  steam  or  exhaust  lap,  or  in 
the  angular  advance  d  are  readily  examined  by  the  aid  of  this 
diagram,  and  will  be  found  to  agree  with  the  statements  of  the 
table  in  [2] . 

[4]  £etiner  Valve  Diagram. 

In  Fig.  227  let  ABCD  be  a  circle  described  with  radius  OA 
equal  to  the  throw  of  the  excentric.  Let  A  denote  the  angular 
position  of  the  crank  at  the  end  of  the  stroke,  and  let  OB  be 
drawn  perpendicular  to  AC.  Draw  OP  at  the  angle  <5  (the  angu- 
lar advance)  with  OB,  and  on  OP  as  diameter  describe  a  circle  as 
shown.  Draw  also  an  arc  of  a  circle  with  OL  equal  to  the  steam 
lap,  as  radius.  Let  OAn  be  any  position  of  the  crank.  Then 
the  properties  of  this  diagram  are  such  that  the  travel  of  the 
valve  from  mid  position  is  given  by  the  distance  OG,  while  the 
port  opening  will  of  course  be  given  by  EG  the  intercept  between 
this  circle  and  the  lap  circle  MN.  A  similar  construction  holds 
for  other  locations  of  the  crank,  and  it  thus  appears  that  steam 
opening  will  occur  at  N  with  the  crank  in  the  position  ON 
while  closure  or  cut-off  will  occur  at  M  with  the  crank  in  the  po- 
sition OM.  By  describing  a  circle  with  center  at  O  and  with 
radius  equal  to  the  exhaust  lap,  a  similar  construction  gives  the 


380  PRACTICAL  MARINE  ENGINEERING. 

various  features  of  the  movement  on  the  exhaust  side  of  the 
valve.  The  history  of  the  port  opening  for  steam  is  thus  given 
~by  the  intercepts  between  MN  and  the  circle  on  OP,  as  shown  by 
the  shaded  part  of  the  diagram. 

In  case  the  width  of  port  is  less  than  the  distance  LP  an  arc 
RQ  is  drawn  from  O  as  center  such  that  the  radial  distance  be- 
tween MN  and  RQ  equals  the  width  of  port.  The  history  of  the 
port  opening  is  then  given  in  the  same  way  as  for  the  corre- 
sponding case  in  Fig.  226,  as  there  explained. 

The  results  of  a  change  in  the  steam  or  exhaust  lap,  or  in 
the  angular  advance  #,  are  readily  examined  by  the  aid  of  this 


Fig.  227.     Zeuner  Valve  Diagram. 

diagram,  and  will  be  found  in  accord  with  the  statement  of  the 
table  in  [2] . 

Sec.  48.    STEPHENSON  I/INK  VAIfVE  GEAR. 

We  have  thus  far  examined  in  some  detail  the  operation  of 
a  slide  valve  operated  by  a  single  excentric.  In  the  course  of 
the  discussion  it  has  appeared  that  with  such  a  gear  the  direction 
of  motion  of  the  crank  relative  to  the  excentric  depends  on 
whether  the  valve  takes  steam  on  the  inside  or  outside,  and  on 
the  nature  of  the  connection  between  the  excentric  rod  and 
valve  stem.  With  any  one  arrangement,  however,  motion  in  one 
direction  only  is  possible ;  and  it  is  therefore  clear  that  to  enable 


VALVES  AND   VALVE  GEARS.  381 

the  engine  to  reverse — a  fundamental  requirement  of  all  marine 
valve  gears — some  additional  features  will  be  necessary. 

The  general  problem  of  a  reversing  valve  gear  is  one  which 
has  been  solved  in  a  great  variety  of  ways,  both  with  and  with- 
out the  use  of  excentrics,  as  we  shall  see  later.  With  the  use 
of  excentrics  the  simplest  solution  is  furnished  by  the  well-known 
Stephenson  link.  This  is  illustrated  geometrically  in  Fig.  228. 
C  represents  the  crank  on  the  center.  A  denotes  one  excentric 
at  an  angle  COA  on  one  side  of  the  crank  and  B  another  at  the 
same  or  approximately  the  same  angle  COB  on  the  other  side. 
AD  and  BE  denote  two  excentric  rods  connected  by  a  link  DE 
curved  to  an  arc  whose  radius  is  the  length  of  the  rod  AD  or  BE. 
To  a  block  in  this  link  is  attached  the  valve  stem  DG.  For  the 
structural  details  of  this -gear  reference  may  be  made  to  Sec.  53. 


Marine  Engineering 

Fig.  228.     Skeleton  of  Stephenson  Link. 

Now  it  will  be  readily  seen  that  with  the  arrangement  of  the 
diagram  the  valve  is  under  the  control  of  the  excentric  A  alone. 
The  excentric  B  simply  pulls  the  link  DE  back  and  forth,  causing 
it  to  swing  about  D,  but  in  no  way  affecting  the  movement  of 
the  valve.  Hence  the  engine  will  move  entirely  under  the  con- 
trol of  the  excentric  A,  and  with  an  outside  valve  direct  con- 
nected, the  direction  of  rotation  will  be  right-handed,  or  from  C 
toward  A.  Now  to  effect  the  reverse,  it  is  only  necessary  to 
move  the  link  over  so  that  E  comes  to  the  center  line  and  the 
valve  and  engine  pass  under  the  control  of  the  excentric  B  alone. 
For  the  reasons  already  noted  in  Sec.  47  [i]  the  motion  will 
now  be  reversed  and  the  rotation  will  be  left-handed  or  from 
C  toward  B. 


382  PRACTICAL  MARINE  ENGINEERING. 

We  have  next  to  tequire  regarding  the  motion  of  the  valve 
stem  when  the  link  is  only  part  way  over,  as  shown  by  the 
broken  lines  in  the  diagram.  In  such  case  it  is  readily  seen  that 
the  motion  of  the  valve  will  be  derived  partly  from  the  excentric 
A  and  partly  from  B,  the  former  giving  the  principal  part  ot 
the  motion,  and  the  latter  exercising  a  modifying  influence.  Now 
without  taking  up  the  examination  of  this  question  in  detail,  it 
will  be  sufficient  to  state  that  within  a  very  small  error  the  result- 
ant motion  will  be  the  same  as  though  it  were  given  by  a  single 
excentric  of  somewhat  decreased  throw  ,and  increased  angular 
advance  as  compared  with  A  or  B.  A  simple  construction  will 
serve  to  determine  the  throw  and  angular  advance  of  this  equiva- 
lent single  excentric.  This  may  be  carried  out  as  follows : 

(1)  In  Fig.  229  lay  off  the  two  excentric  throws  OA  and  OB, 
with  the  proper  angular  advance  as  shown,  and  draw  the  line  AB. 

(2)  Divide  the  length  of  the  link  DE  Fig.  228  by  twice  the 
excentric  rod  AD  and  multiply  the  quotient  by  the  length  AC 
Figr'  229. 

(3)  Lay  off  the  result  from  C  to  D,  and  through  the  three 
points  A  D  B  pass  the  arc  of  a  circle,  as  shown. 

Then  the  arc  ADB  may  be  considered  as  representing  the 
link,  and  to  find  the  throw  and  angular  advance  of  the  equivalent 
excentric  for  any  given  position  of  the  link-block  as  F  on  D  l  E  l . 
Fig.  228,  we  have  only  to  take  a  corresponding  point  F  on  the 
arc  ADB,  and  draw  the  radius  OF.  The  throw  is  then  repre- 
sented by  OF  and  the  angular  advance  fi  by  the  angle  POF. 

That  is,  if  the  link  be  put  into  the  position  shown  by  broken 
lines  in  Fig.  228  the  movement  of  the  valve  will  be,  within  a  small 
error,  the  same  as  though  it  were  operated  by  a  single  excentric 
of  throw  OF,  Fig.  229  and  angular  advance  POF  determined 
in  the  manner  described.  It  is  readily  seen,  therefore,  that  as 
the  link  is  so  moved  as  to  bring  the  block  from  the  end  nearer 
and  nearer  the  center,  the  corresponding  point  F  Fig.  229  will 
move  from  A  nearer  and  nearer  to  D,  and  the  throw  of  the 
equivalent  excentric  will  continually  decrease  while  the  angular 
advance  will  increase.  As  the  link  passes  the  center  and  the 
block  approaches  the  other  end  the  corresponding  point  F  moves 
on  from  D  toward  B,  and  the  throw  again  increases,  while  the 
angular  advance  changes  to  the  other  side  and  gradually  de- 
creases as  B  is  approached.  With  the  link  in  full  gear  at  either 
end,  the  corresponding  point  F  comes  to  either  A  or  B,  and  the 


VALVES  AND  VALVE  GEARS. 


383 


equivalent  excentric  becomes  the  same  as  the  real  excentric, 
with  its  throw  and  angular  advance  as  constructed. 

In  some  cases,  especally  with  the  double-bar  form  (see  Sec. 
53)  the  link  may  be  put  over  so  as  to  bring  the  block  even  be- 
yond the  points  of  attachment  of  the  excentric  rods.  See  Fig. 
243.  In  such  case  the  throw  and  angular  advance  of  an  equi- 
valent excentric  will  be  given  by  extending  the  arc  beyond 
A  and  B  as  shown  in  Fig.  229,  and  by  then  taking  a  point  F  cor- 
responding to  the  relative  location  of  the  block  and  link.  In  such 
case  it  is  seen  that  the  throw  is  increased  and  the  angular  ad- 
vance decreased. 

The  details  of  the  motion  for  any  given  position  of  the  link- 
block  may,  of  course,  be  determined  by  the  use  of  any  of  the 


Fig.  229.     Construction  for  Equivalent  Excentric — Stephenson  Link. 

methods  given  above  for  the  case  of  a  single  excentric.  It  is 
simply  necessary  to  take  the  equivalent  throw  and  angular  ad- 
vance determined  as  in  Fig.  229,  and  use  them  according  to  the 
methods  described  in  Sec.  47.  In  this  way  it  may  be  found  that 
as  the  gear  is  linked  up,  or  the  block  approaches  the  middle,  the 
valve^  travel  and  port  openings  decrease,  the  lead  increases,  and 
the  cut-off  becomes  earlier.  This  is  further  illustrated  by  the  two 
oval  diagrams"  of  Fig.  230.  These  are  constructed  as  explained 
in  Sec.  47  [2],  and  represent  the  effect  of  linking  up.  The 
larger  diagram  represents  the  movement  for  full  gear  position 
as  shown  by  the  full  lines  of  Fig.  228,  while  the  smaller  and 
narrower  one  represents  that  for  a  linked  up  position  as  shown 
by  the  broken  lines  of  the  same  diagram. 


384 


PRACTICAL  MARINE  ENGINEERING. 


A  gear  arranged  as  in  Fig.  228  is  known  as  an  open  gear  or 
gear  with  open  rods.  That  is  when  the  crank  is  turned  away 
from  the  cylinder  the  rods  are  open  as  shown.  If  instead  of 
this  the  rods  are  crossed  as  shown  in  Fig.  231,  then  it  is  called  a 
gear  with  crossed  rods.  It  will  be  noted  that  with  the  open  gear 
the  rods  become  crossed  when  the  crank  is  turned  toward  the 
cylinder,  while  in  the  same  position  the  rods  in  the  crossed  gear 
become  open.  It  is  therefore  necessary  to  note  the  character  of 
the  gear  by  the  appearance  of  the  rods  when  the  crank  is 
turned  away  from  the  cylinder  as  stated  above.  It  must  now 
be  remembered  that  the  construction  given  in  Fig.  229  and  the 


Fig.  230.     Oval  Valve  Diagrams  for  Stephenson  Link. 

conclusions  drawn  from  it  apply  to  the  gear  with  open  rods 
only.  For  the  crossed  rod  gear,  however,  a  similar  construc- 
tion applies  as  shown  in  Fig.  232.  The  distance  CD  is  here  laid 
off  toward  the  center  and  a  like  arc  is  passed  through  the  three 
points  ADB  as  shown.  The  diagram  thus  constructed  is  used  in 
the  same  manner  as  with  Fig.  229.  It  is  thus  seen  as  the  link- 
block  approaches  the  center  of  the  link  and  the  corresponding 
point  F  approaches  D,  that  the  equivalent  angular  advance  in- 
creases, the  equivalent  throw,  valve  travel  and  port  openings 
decrease,  even  more  rapidly  than  with  the  open  gear,  while 
the  lead  decreases  and  the  cut-off  is  earlier  and  earlier. 

The  principal  characteristics  of  these  two  types  of  Stephen- 
son  link  valve  gear  with  regard  to  the  effect  on  the  various 
events,  etc.,  due  to  linking  the  gear  up  may  be  conveniently  pre- 
sented in  the  following  tabular  form  : 


VALVES  AND  VALVE  GEARS. 


385 


STEPHENSON   LINK. 

EFFECT    OF    LINKING    UP. 


Type  of  Gear. 


Open  Rods. 


Crossed  Rods. 


Equivalent    Excentric  Throw         Decreased 

Angular  Advance  Increased 

Valve  Travel  Decreased 

Port  Opening  Decreased 

Lead  Increased 

Cut-Off  Earlier 


Decreased 
Increased 
Decreased 
Decreased 
Decreased 
Earlier 


Fig.  231.     Skeleton   of    Stephenson    Link,    Crossed    Rods. 


Fig.  232.     Construction    for    Equivalent    Excentric    with    gear   of  Fig.   231. 

The  chief  point  of  difference  is  seen  to  be  in  the  lead,  which 
increases  with  open  rods  and  decreases  with  crossed  rods  as  the 
gear  is  linked  up.  While  both  types  of  gear  are  met  with,  the 
open  rod  gear  is  more  frequently  employed.  This  is  due  to  the 
fact  that  as  the  cut-off  is  made  earlier  by  linking  up,  an  increase 


386  PRACTICAL  MARINE  ENGINEERING. 

of  lead  may  be  preferred  to  a  decrease,  and  also  to  the  fact  that 
the  width  of  port  opening  is  decreased  less  rapidly  by  the  open 
than  by  the  crossed  gear. 

Sec.  49.  BRAEMME-MARSHAI,!,  GEAR. 

The  Stephenson  link  is  by  no  means  the  only  form  of  valve 
gear  which  will  allow  of  reversal  and  which  will  give  variable 
cut-off.  Among  the  other  arrangements  are  several  known  as 
"radial  valve  gears,"  and  of  these  the  more  important  may  be 
briefly  described. 

In  Fig.  233  let  C  denote  the  position  of  the  crank  and  E 
the  position  of  a  single  excentric  located  directly  opposite  the 
crank.  Let  FD  be  a  slide  pivoted  on  the  horizontal  line  OX, 
and  EB  a  rod  attached  to  the  excentric  at  E  and  fitted  with  a 
pin  joint  and  block  at  P  so  that  the  block  may  move  in  orAon 
the  slide  FD.  Then  as  the  excentric  moves  around  O  the  end 
E  of  the  rod  describes  a  circle,  the  point  P  describes  a  straight 
line  FD  back  and  forth,  and  other  points  between  P  and  E 
describe  paths  intermediate  between  these  two.  For  a  point 
such  as  Q  this  is  found  to  be  an  inclined  oval  as  shown  in  the 
diagram.  For  points  beyond  P  such  as  Q',  for  example,  the 
path  is  found  to  be  a  somewhat  similar  oval  as  shown.  Now 
it  is  found  that  the  proper  motion  for  a  valve  can  be  derived 
from  a  point  moving  as  Q  or  Q'  and  that  it  is  simply  necessary 
to  connect  such  point  by  a  proper  link  to  the  valve  stem  as 
shown  for  Q. 

Instead  of  placing  the  excentric  at  180  degrees  from  the 
crank  it  may  be  placed  with  the  crank,  in  which  case  in  Fig.  233 
we  should  consider  the  crank  at  C'.  There  are  thus  four  arrange- 
ments of  the  gear  according  as  the  excentric  is  with  or  opposite 
the  crank,  and  as  the  point  Q  is  between  P  and  E  or  beyond  P. 

In  all  cases  the  gear  must  be  so  adjusted  that  when  the 
crank  is  on  either  center  as  C,  the  point  P  is  on  OX,  or  at  the 
pivotal  point  of  FD.  It  is  readily  seen  that  if  this  condition  is 
fulfilled  for  one  center  it  will  be  likewise  for  the  other. 

With  regard  to  the  kind  of  valve  to  be  used  (inside  or  out- 
side) and  the  direction  in  which  the  engine  will  run  for  any  given 
arrangement  of  gear,  the  same  principles  may  be  applied  as  in 
the  case  of  the  single  excentric.  Thus  it  is  easily  seen  from  the 
symmetry  of  the  motion  that  Q  will  go  as  far  above  the  center 
line  as  below,  and  hence  that  OX  contains  the  middle  of  its 


VALVES  AND  VALVE  GEARS. 


387 


vertical  motion.  Hence  in  the  arrangement  of  the  figure  with 
the  crank  on  the  top  center  the  valve  is  below  its  mid  position 
by  the  distance  from  Q  to  the  center  line  OX.  Hence  to  take 
steam  on  the  top  of  the  piston  an  outside  valve  must  be  em- 
ployed, and  the  engine  will  go  in  the  direction  which  will  open 


Fig.  233.     Braemme    Marshall    Radial    Valve    Gear. 

the  valve  still  wider.  This  must  be  that  which ^will  lower  the  valve, 
and  hence  that  which  will  lower  P,  and  hence  that  which  will 
carry  E  to  the  left,  or  right-hand  rotation.  If,  on  the  other 
hand  the  motion  were  derived  from  Q',  the  valve  will  be  above 


388  PRACTICAL  MARINE  ENGINEERING. 

its  mid  position,  and  hence  to  take  steam  on  top  it  must  be  an 
inside  valve.  The  engine  in  this  case  will  turn  in  the  direction 
which  will  raise  Q'  still  further.  This  requires  E  to  move  to  the 
right,  and  hence  the  rotation  will  be  left-handed. 

If  FD  be  inclined  in  the  other  direction,  as  shown  by  the 
dotted  line,  it  will  be  readily  seen  by  the  same  rule  that  the 
direction  of  rotation  in  each  case  will  be  reversed.  It  is  also 
found  that  as  the  direction  of  FD  approaches  the  horizontal  or 
OX,  the  cut-off  becomes  earlier  and  earlier,  and  it  is  readily 
seen  that  the  valve  travel  and  hence  the  port  opening  will  de- 
crease. We  have  here  therefore  an  entirely  similar  action  to 
that  which  takes  place  in  linking  up  with  the  Stephenson  link. 
The  means  for  changing  the  cut-off  and  for  reversal  are  there- 
fore furnished  by  providing  a  means  for  changing  or  reversing 
the  obliquity  of  the  slide  FD,  and  for  retaining  it  in  any  position 
desired. 

Since  the  point  P  comes  to  the  center  of  the  slide  or  pivot 
point  when  the  engine  is  on  the  center,  it  follows  that  in  this 
position  the  line  EB,  the  point  Q  and  the  valve  will  have  exactly 
the  same  location  no  matter  what  the  position  of  FD,  and  hence 
no  matter  what  the  point  of  cut-off.  Hence  the  lead  of  the 
valve  will  be  the  same  for  all  points  of  cut-off,  or  in  other  words, 
the  lead  is  not  affected  by  the  change  in  cut-off.  This  is  a 
feature  which,  as  we  shall  see,  is  possessed  by  the  various  forms 
of  radial  valve  gear.  With  the  Stephenson  link  the  lead  is  vari- 
able with  the  cut-off  as  described  in  Sec.  48. 

As  noted  above  there  are  four  arrangements  of  this  gear 
depending  on  the  location  of  the  point  Q,  and  the  angle  between 
the  excentric  and  the  crank. 


Location  of  Q.  Valve. 


o 

Inside  P 

Inside. 

180° 

Inside  P 

Outside. 

o 

Outside  P 

Outside. 

1  80° 

Outside  P 

Inside. 

These  four  arrangements  are  shown  in  the  above  table 
with  the  appropriate  form  of  valve.  The  direction  of  rotation 
in  each  case  will  depend  of  course  upon  the  direction  of  obli- 
quity of  the  slide  FD. 


VALVES  AND  VALVE  GEARS. 


389 


The  arrangement  of  Fig.  233  shows  the  earlier  form  of  the 
gear.  Another  and  later  form  is  shown  in  Fig.  234  in  which 
the  slide  FD  Fig.  233  is  replaced  by  an  arm  Pl\  pivoted  at  Tl9 
and  attached  by  a  wrist  pin  to  the  rod  EB.  In  this  way  the  point 
P  is  caused  to  move  in  the  arc  of  a  circle  Fl  Dl  inclined  to  the 


Fig.  234.     Braemme    Marshall    Radial    Valve    Gear. 

horizontal  OX  as  shown.  In  such  case  the  motion  of  the  valve 
is  very  nearly  the  same  as  if  the  point  P  moved  in  the  line  of  the 
tangent  F  D,  and  except  for  secondary  modifications  it  is  there- 
fore equivalent  to  the  motion  of  Fig.  233.  The  change  of  cut-off 
and  the  reversal  are  brought  about  by  swinging  the  pivot  Tx 


390 


PRACTICAL  MARINE  ENGINEERING. 


about  a  center  S,  the  intersection  of  FD  with  OX.  In  this  way 
Tj  is  brought  to  a  new  position  T2  and  the  line  of  motion  is 
brought  to  F2  D2,  thus  reversing  the  direction  of  rotation  ac- 
cording to  the  same  principles  as  applied  in  the  preceding  case. 


; 

• 

I 

,r\ 

•N\  i 

1  \ 

\ 

i    1 

\ 

1    1 

1 

U-a 

Fig.  235.    Joy    Radial    Valve    Gear. 

We  may  evidently  have  here  the  same  four  arrangements  as  in 
the  other  form  of  the  gear,  with  the  same  relation  between  ex- 
centric  angles  and  type  of  valve  as  given  in  the  table  above. 


VALVES  AND   VALVE  GEARS.  29' 

Sec.  50.    JOY  VAI,VE  GEAR. 

In  this  form  of  radial  valve  gear  no  excentric  whatever  is 
required.  As  shown  in  Fig.  235  F  is  a  point  on  the  connecting 
rod  to  which  a  link  DF  is  attached  pivoted  to  a  swinging  or  sus- 
pension bar  DK.  The  point  F  moves  in  an  oval  path  as  shown. 
The  point  D  moves  in  the  arc  of  a  circle  as  shown.  An  inter- 
mediate point  as  E  will  move  in  a  path  somewhat  as  shown. 
From  this  point  on,  the  gear  is  similar1  to  a  Braemme-Marshall. 
Thus  EP  is  a  link  pivoted  at  E  and  with  the  point  P  carried  by 
a  suspension  bar  PR  exactly  the  same  as  PT  of  Fig.  234.  The 
motion  for  the  valve  is  similarly  taken  from  a  point  Q  as  shown. 
It  is  thus  clear  that  the  Joy  gear  as  here  shown  is  the  gear  of 
Fig.  234  in  which,  however,  the  point  E  instead  of  moving  in  a 
circular  path  derives  its  motion  from  the  connections  shown  in 
Fig-  235  and  moves  in  a  distorted  oval  path  as  there  shown. 
It  is  clear  that  there  will  be  the  same  two  varieties  of  gear  ac- 
cording as  the  point  Q  is  taken  between  E  and  P  or  beyond  P. 
The  reversal  is  also  effected  in  the  same  fashion  by  swinging 
PR,  or  the  straight  slide  may  be  used  as  in  the  gear  shown  in 
Fig-  233. 

Sec.  51.    WAI,SCHAERT  VAI,VE  GEAR. 

In  this  gear  as  shown  in  outline  in  Fig.  236,  one  excentric 
E  is  used.  MGK  is  a  curved  link  pivoted  at  G.  H  is  a  block 
sliding  on  or  in  the  link  and  connected  by  a  radius  arm 
to  the  valve  lever  AF.  The  end  F  of  this  lever  is  connected  by 
a  pin  joint  to  the  valve  rod,  and  the  other  end  A  by  a  short  link 
to  the  main  crosshead  as  shown.  The  valve  is  thus  seen  to  de- 
rive its  motion  in  part  from  the  main  crosshead  and  in  part  from 
the  excentric.  The  former  part  comes  through  the  valve  lever 
which  pivots  about  D  and  thus  communicates  motion  from  C  to 
F.  The  latter  part  comes  from  the  curved  link  which  is  operated 
by  the  excentric,  causing  it  to  swing  about  G  and  thus  through 
the  radius  arm  and  valve  lever  the  motion  of  the  excentric  is 
communicated  to  the  valve  rod.  The  combination  of  these  two 
motions  is  found  to  be  such  as  to  give  a  suitable  movement  to 
the  valve. 

The  linking  up  and  reversal  are  accomplished  by  swinging 
the  block  H  and  radius  rod  from  one  side  to  the  other  of  the 
mid-position  or  pivot  G.  As  the  block  H  is  brought  nearer  to  G 
the  cut-off  becomo*  earlier  while  the  valve  travel  and  port-open- 


392 


PRACTICAL  MARINE  ENGINEERING. 


ing  are  decreased  the  same  as  with  the  Stephenson  link  above 
described. 

In  order  that  this  gear  may  operate  properly,  certain  ad- 
justments are  required  as  follows: 

The  radius  of  the  curved  link  MGK  must  equal  the  radius- 
rod  HD. 

Place  the  crank  on  say  the  top  center,  and  bring  the  link 


Fig.  236.     Walschaert  Valve  Gear. 

MGK  into  line  with  an  arc  struck  from  D  as  center  with  DH 
as  radius.  Then  M  should  be  so  taken  that  the  angle  OMG  is 
a  right  angle.  Also  the  excentric  E  is  placed  at  a  right  angle 
from  OM  as  shown.  Then  in  this  position  the  block  H  may 
be  drawn  to  and  fro  along  the  link  without  moving  the  valve. 
It  is  also  clear  that  after  the  crank  has  gone  180  degrees  the 
excentric  will  be  at  E,  and  MG  will  be  again  in  the  same  position 


VALVES  AND  VALVE  GEARS.  393 

and  the  block  H  may  be  drawn  along  the  link  without  giving 
motion  to  the  valve.  It  follows  that  the  position  of  the  valve 
when  the  crank  is  on  the  centers  will  be  the  same  no  matter 
where  the  block  H  may  be  located,  and  hence  that  the  lead 
of  the  valve  will  be  the  same  for  all  points  of  cut-off. 

It  is  clear  that  the  arrangement  of  Figs.  233-236  will  bring 
the  valve  chest  on  the  side  of  the  cylinder  transversely  instead 
of  fore  and  aft.  The  cylinders  may  therefore,  so  far  as  valve 
chests  are  concerned,  be  placed  nearer  together  than  with  the 
Stephenson  link,  in  which  case  the  valve  chests  are  forward  or 
aft  of  the  cylinders.  The  length  of  the  engine  as  a  whole  may 
therefore  be  made  somewhat  less  with  the  radial  types  of  gear 
than  with  the  Stephenson  link,  and  it  is  this  feature  which  gives 
to  them  their  best  claim  of  advantage.  Such  gears  possess 
also,  as  we  have  seen,  the  property  of  giving  the  same  lead  for 
all  points  of  cut-off,  while  with  the  Stephenson  link  the  lead 
varies  with  the  cut-off.  With  proper  design,  however,  the  varia- 
tion in  the  latter  case  is  not  sufficient  to  constitute  a  feature  of 
any  importance,  and  the  difference  on  this  point  can  hardly  be 
considered  as  forming  any  noteworthy  advantage  for  the  radial 
gears.  The  general  character  of  the  valve  movement  and  the 
distribution  of  events  in  all  cases  is  best  studied  by  the  aid  of  a 
diagram  such  as  that  of  Fig.  223.  It  will  thus  be  found  that  the 
results  for  these  various  cases  will  be  quite  similar,  and  that 
such  differences  as  appear  are  of  relatively  small  importance. 
Speaking  broadly,  it  is  perhaps  fair  to  say  that  there  is  not  suffi- 
cient difference  in  the  operation  of  the  valve  itself  to  furnish 
any  pronounced  claim  of  advantage  for  the  usual  cases  arising 
in  marine  practice.  The  choice  must  therefore  be  made  rather 
by  reason  of  structural  considerations,  such  as  the  shortening 
up  of  the  engine  referred  to  above,  or  the  details  of  construction 
of  the  gear  as  affecting  the  questions  of  breakage,  wear  and 
tear,  readiness  of  repair,  readjustment,  etc.  On  the  whole,  the 
Stephenson  link  seems  to  be  usually  preferred  as  the  best  ful- 
filling the  all  around  requirements  for  the  marine  valve  gear, 
and  it  may  be  fairly  considered  as  the  representative  gear  in 
present-day  marine  practice. 

Sec.  52-     CRANK  VAI,VE  GEAR. 

As  we  have  seen  in  Sec.  47  [i]  the  action  of  an  excentric 
is  equivalent  to  that  of  a  simple  crank  of  throw  equal  to  the 


394 


PRACTICAL  MARINE  ENGINEERING. 


excentric  and  set  at  a  corresponding  angle  with  the  main  crank. 
It  is  evident  then  that  a  series  of  cranks  will  operate  a  valve 
and  gear  in  a  manner  identical  with  a  corresponding  series  of 
excentrics.  Such  cranks,  however,  on  account  of  their  small 
throw  cannot  readily  be  located  or  formed  on  the  main  crank- 
shaft, and  hence  where  used  for  operating  the  valves,  are  neces- 
sarily placed  on  a  special  or  auxiliary  shaft.  In  Fig.  237  is  shown 
the  usual  way  of  arranging  the  parts  of  this  gear. 

S  is  the  center  of  the  main  crank-shaft,  and  ST  the  main 
crank.  A,  B,  and  C  are  gear  wheels,  A  attached  to  the  crank- 
shaft, B  an  idler,  and  C  attached  to  the  valve  shaft.  O  is  the 
center  of  this  shaft  and  OP  represents  the  throw  and  angulai 
location  of  the  small  crank  for  operating  the  valve.  The  valve 


Fig.  237.    Crank    Valve    Gear. 

shaft  will  then  turn  in  the  same  direction  as  the  main  shaft,  and 
as  may  be  readily  seen,  will  operate  the  valve  precisely  in  the 
same  manner  as  an  ordinary  excentric  of  the  same  throw  and 
angular  location.  For  reversing  with  this  gear  the  usual  plan 
is  to  have  but  one  crank  and  valve-connecting-rod  correspond- 
ing to  one  excentric  rod.  The  angular  location  of  the  crank 
must  then  be  changed  from  a  position  such  as  OP  in  the  figure 
to  OPj.  By  comparing  this  with  Sec.  47  [i]  it  is  seen  that  such 
a  change  in  the  location  of  the  crank  will  necessarily  cause  the 
engine  to  move  in  the  opposite  direction.  To  bring  about  this 
change  in  the  location  of  the  valve  crank  relative  to  the  main 
crank,  various  mechanical  devices  may  be  used. 

Thus  it  may  be  seen  that  if  after  the  engine  has  stopped 


VALVES  AND  VALVE  GEARS. 


395 


the  gear  C  were  slipped  out  of  the  mesh  with  B,  turned  around 
through  the  angle  POP  l  and  then  slipped  back  into  mesh  again, 
the  crank  would  be  brought  to  OP  l  and  if  the  engine  were 
started  again  it  would  go  in  the  opposite  direction.  This,  of 
course,  is  not  a  practicable  form  of  reverse,  since  it  cannot  be 
carried  out  quickly  enough,  nor  when  the  engine  is  in  motion. 
It  does,  however,  serve  to  illustrate  the  necessary  change  to  be 
made  in  the  angular  location  of  OP. 

In  the  usual  mode  of  operation,  some  form  of  spiral  cam  is 
employed,  as  illustrated  in  Fig.  238.  C  is  the  gear  wheel  car- 
ried on  a  sleeve  AB  and  connected  to  it  by  a  key  way  and 
feather  so  that  the  sleeve  may  be  moved  back  and  forth  axially 
and  still  remain  coupled  to  the  gear  C  so  far  as  rotary  motion  is 
concerned.  The  gear  C  is  also  prevented  by  suitable  stops  from 
being  carried  out  of  mesh  with  the  gear  B,  Fig.  237.  This  sleeve 
is  carried  on  the  shaft  D  to  which  is  attached  the  valve  crank, 


Fig.  238.     Crank  Valve   Gear,   Reversing  Arrangement. 

and  is  loose  on  D  and  only  connected  with  it  by  a  pin  P  which 
projects  through  a  spiral  groove  RS  cut  in  the  metal  of  the 
sleeve.  At  E  there  is  a  circumferential  groove  in  the  sleeve,  in 
which  is  fitted  the  end  of  a  controlling  lever  F,  by  means  of 
which  the  sleeve  may  be  moved  back  and  forth  longitudinally. 
In  the  figure  the  sleeve  is  shown  pushed  in  so  that  the  pin  is  at 
one  extremity  of  its  travel  in  the  spiral  groove,  and  the  valve- 
crank  will  therefore  be  in  a  corresponding  position  with  refer- 
ence to  the  gear  C  and  main  crank,  which  we  will  suppose  to  be 
for  full  gear  ahead.  If  now  the  sleeve  be  pulled  longitudinally 
until  the  other  end  of  the  groove  contains  the  pin,  it  is  clear 
that  we  shall  have  changed  the  angular  location  of  the  pin  rela- 
tive to  the  gear  and  hence  of  the  valve-crank  relative  to  the 
main  shaft.  If  then  the  spiral  groove  be  of  suitable  extent  and 
location,  such  a  change  will  serve  to  move  the  crank  OP,  Fig. 


396  PRACTICAL  MARINE  ENGINEERING. 

237,  from  its  position  for  full  gear  ahead,  to  OP^  its  position  for 
full  gear  astern.  Instead  of  one  pin  and  spiral  groove,  two  on 
opposite  sides  may  be  used,  and  other  details  may  vary  in  many 
ways,  but  the  arrangement  will  serve  to  illustrate  the  principles 
involved. 

While  this  form  of  valve  gear  is  thus  efficient  for  reversing,  it 
is  much  less  suitable  for  linking  up  or  varying  the  cut-off  than 
the  other  forms  of  gear  discussed  above.  Referring  to  Sec.  48  it 
was  there  shown  how  to  find  the  equivalent  simple  excentric  for 
any  adjustment  of  the  Stephenson  link,  as  shown  by  the  line 
A  D  B,  Fig.  229,  for  an  open  rod  gear.  Now  it  is  readily  seen 
that  the  form  of  reverse  just  considered  is  equivalent  to  taking 
the  excentric  O  A  and  carrying  it  around  from  OA  to  OB,  so 
that  for  the  varying  intermediate  positions  the  virtual  excentric 
would  be. given  by  drawing  a  line  from  O  to  the  arc  A  B  with 
OA  as  radius.  From  the  principles  discussed  in  Sec.  47  [2]  it 
is  readily  seen  that  the  effect  on  the  valve  will  be  as  follows  : 

Linking  up  will  produce  : — 

Earlier  cut-off. 

Earlier  steam  opening. 

Greatly  increased  lead. 

Earlier  exhaust  opening. 

Earlier  and  greater  compression. 

The  same  valve  travel  and  opening. 

While  therefore  the  port  opening  is  not  decreased  by  link- 
ing up,  the  lead  and  compression  may  become  excessive,  and  re- 
strict the  practicable  range  of  variable  cut-off  to  narrow  limits. 

In  Fig.  237  we  have  referred  to  one  cylinder  and  valve  op- 
erating crank  only,  but  the  same  arrangement  may  be  applied,  of 
course,  to  a  series  of  cylinders  for  a  multiple  expansion  engine. 
In  such  case  the  valve  operating  shaft  has  a  series  of  cranks,  one 
for  each  cylinder,  and  set  at  the  proper  angle  from  the  corre- 
sponding main  crank.  Then  with  a  reverse  gear  similar  to  that 
described  in  Fig.  238  all  the  cranks  are  moved  together  and  are 
brought  into  the  proper  relation  with  their  main  cranks  to  oper- 
ate the  engine  in  the  reverse  direction. 

It  is  also  to  be  noted  that  this  arrangement  brings  the  valve 
chests  at  the  sides  of  the  cylinders  and  that  on  this  account  it  has 
the  same  effect  in  shortening  up  the  engine  as  the  use  of  a 
radial  valve  gear.  This  type  of  gear  has  been  used  to  some 
extent  on  launch,  yacht  and  torpedo  boat  engines,  but  has  not 


VALVES  AND  VALVE  GEARS. 


397 


found  favor  for  larger  or  slower  running  engines  as  used  in  ordi- 
nary mercantile  and  naval  practice. 

Sec.  53.  DETAILS  OF  STEPHENSON  LINK  VALVE  GEAR. 

In  the  present  section  we  shall  give  a  brief  description  of 
the  more  important  details  of  the  Stephenson  Link  valve  gear  as 
a  representative  gear,  and  including  as  it  does  most  of  the  ele- 
ments of  other  forms  of  gear  as  described  in  Sec.  49-52. 

fi]  Excentric  and  Strap  and  Excentric  Rod. 

The  general  construction  of  this  part  of  the  gear  is  shown 
in  Figs.  239-242.  The  excentric  consists  of  a  disc  or  sheave  of 


.. 

! 


Fig. 


Excentric,   Detail   of  Construction  and   Fitting. 


circular  form,  and  placed  on  the  shaft  excentric  or  with  its  cen- 
ter set  out  from  the  center  of  the  shaft.  As  shown  in  the  figure 
the  sheave  is  made  in  two  unequal  halves  which  join  on  the  cen- 
ter line  of  the  shaft,  and  are  secured  by  bolts  as  shown.  This 
brings  the  center  of  the  disc  at  the  point  shown,  the  distance  AB 
between  this  and  the  center  of  the  shaft  being  the  excentric 
throw  as  defined  in  Sec.  47.  'Once  adjusted  the  excentric  is 
keyed  in  place  and  in  addition  set  screws  or  binding  bolts  may 
be  fitted,  as  shown.  In  the  excentric  of  Fig.  239  the  larger  part 
of  the  sheave  is  lightened  out  to  save  weight.  In  excentrics  of 
moderate  size  this  is  not  usually  done,  and  the  bolts  connecting 


398 


PRACTICAL  MARINE  ENGINEERING. 


the  two  parts  are  tapped  into  the  larger  part  and  hold  the  other 
portion  in  place  by  means  of  a  countersunk  head.  The  material 
of  the  excentric  is  either  cast-iron  or  steel,  or  if  small  in  size, 
^brass  is  sometimes  employed. 

The  strap  which  surrounds  the  excentric  as  shown  in  Fig. 
240  is  also  made  in  two  parts  bolted  together,  and  the  excentric 
rod  is  attached  by  a  flanged  foot  to  the  upper  half  as  shown  in 
the  figure.  There  are  several  ways  of  fitting  the  surfaces  of  the 
strap  and  excentric  together,  as  shown  in  Fig.  241.  In  modern 


Fig.  240.    Excentric   Strap,    Detail    of   Construction   and   Fitting. 

practice  the  strap  is  usually  of  cast-steel  or  brass,  lined  with 
white  metal  for  a  bearing  surface  as  shown  at  a  and  described  in 
Sec.  21  [n]. 

With  this  arrangement  of  excentric  sheave  and  strap,  it  is 
readily  seen  that  as  the  former  turns  with  the  shaft  the  center 
of  the  sheave  turns  about  the  center  of  the  shaft ;  also  that  the 
center  line  of  the  excentric  rod  which  will  always  pass  through 
the  center  of  the  sheave,  will  therefore  move  exactly  as  though 
it  were  a  connecting  rod  with  the  distance  A  B  between  the  two 


VALVES  AND  VALVE  GEARS. 


399 


centers  as  a  crank  arm.  Hence  as  noted  in  Sec.  47  [i]  the  mo- 
tion communicated  to  the  rod  will  be  exactly  the  same  as  would 
be  given  by  a  crank  and  connecting  rod  the  former  of  throw  equal 
to  that  of  the  excentric.  The  other  excentric  strap  and  rod  are 


Fig.  241.'    Different  Methods  of  Fitting  Excentric  Strap. 

fitted  up  in  the  same  manner  and  the  two  rods  connect  with  the 
ends  of  the  link  in  the  manner  shown  in  Fig.  242.  In  this  figure  is 
shown  on  the  left  the  lower  end  of  the  excentric  rod  with 
flange  for  securing  to  the  upper  strap  as  in  Fig.  240.  On  the 


Fig.  242.    Excentric  Rods,  Fittings  at  Ends. 

right  is  shown  the  upper  end  of  the  rod  sometimes  known  as 
the  excentric  rod  fork.  The  form  is  more  properly  that  of  a  U, 
the  two  sides  being  fitted  with  bearing  brasses  and  cap  to  pro- 
vide a  bearing  for  the  pins  by  means  of  which  the  connection 
is  made  with  the  link. 


400 


PRACTICAL   MARINE  ENGINEERING. 


[2] 


In  Fig.  243  is  shown  the  usual  form  of  double  bar  link  as  ft 
is  termed.  It  consists  of  a  pair  of  bars  curved  in  the  arc  of  a 
circle  of  radius  equal  to  the  geometrical  length  of  excentric  rod  ; 
that  is,  equal  to  the  distance  from  the  center  line  of  the  link  to 
the  center  of  the  excentric  sheave.  These  bars  are  connected  at 
the  ends  by  bolts  and  by  a  block  between  so  as  to  main- 
tain the  desired  distance  between  them.  Near  the  ends  are  fitted 
the  pins  A,  B,  C,  D,  which  serve  for  connecting  with  the  excen- 


rrn 

A 

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c 

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LiJ 


Fig.  243.     Stephenson    Double    Bar    Link. 

trie  rods  by  means  of  the  bearings  in  the  upper  ends,  as  shown 
in  Fig.  242.  Another  pair  of  pins  E,  F,  is  fitted,  either  at  the 
center  as  shown  or  as  an  extension  of  the  pairs  at  the  ends,  or  at 
some  intermediate  point.  To  these  are  attached  a  pair  of  bars  or 
links  usually  known  as  side  or  bridle  rods  as  shown  in  Fig.  244. 
These  lead  to  the  rock  or  weigh  shaft,  and  serve  to  control  the 
gear  when  linking  up  or  reversing,  and  to  hold  it  in  any  desired 
position. 

The  rock-shaft  or  weigh-shaft  is  usually  carried  in  bearings 
on  the  outside  of  the  columns  near  the  top,  and  is  provided  with 


VALVES  AND  VALVE  GEARS. 


401 


arms,  one  each  for  the  several  links,  and  one  for  the  connection 
to  the  reverse  cylinder  by  means  of  which  it  is  operated  as  de- 
sired. This  is  sufficiently  illustrated  in  Figs.  100,  116,  247. 

In  order  to  provide  an  independent  adjustment  for  the  valve 


Marine  Eiiyineering 


Fig.  244.    Side  or  Bridle  Rods. 


gear  of  the  different  cylinders,  the  weigh  shaft  arm  as  shown  in 
Fig.  245  may  be  provided  with  a  slot  within  which  moves  a 
block  under  the  control  of  a  hand-wheel  and  screw  as  shown. 
The  bridle  rods  are  attached  to  pins  on  the  sides  of  this  block 


Fig.  245.     Independent   Adjustment   for   Cut   Off  with    Stephenson   Link. 

as  shown  on  the  right,  and  by  this  means  without  moving  the 
weigh  shaft  at  all,  the  links  may  be  given  an  adjustment  within 
the  limits  of  the  motion  of  the  block  in  the  slot.  It  is  custom- 
ary to  so  adjust  the  line  of  motion  of  this  block  that  when  the 


402 


PRACTICAL  MARINE  ENGINEERING. 


g:ear  is  in  the  ex>-ahead  position,  it  shall  lie  nearly  in  the  line  of 
the  bridle  rods  so  that  any  movement  of  the  block  will  be  com- 
municated to  the  link  without  loss.  In  the  backing  position 
on  the  other  hand,  the  line  of  movement  of  the  block  will  lie 
across  the  line  of  the  bridle  rods  at  a  considerable  angle,  and 
movement  of  the  block  back  and  forth  will  give  but  slight  motion 
to  the  link.  See  also  Figs.  100,  247. 

This  arrangement  is  often  of  use  in  adjusting  the  points  of 
cut-off  in  the  separate  cylinders  so  as  to  divide  as  equally  as  pos- 
sible the  power  among  the  different  cylinders.  See  also  Sec.  =55 

[43. 

[3]  I/ink  Block  and  Valve  Stem. 

The  connection  between  the  link  and  the  valve  stem  is 
made  by  means  of  a  link-block  as  shown  in  Figs.  243,  246.  This 


1 


r 

Hi 

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ill 

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£S               .--<—..                cP 

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,-.-t~.         \    i 

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T         '          »  T  I 

i  Jfari'K  Enyineering\ 

Fig.  246.     Link    Block    for    Stephenson    Double    Bar    Link. 

consists  of  a  central  pin  with  wing  pieces  at  the  ends,  as  shown 
in  the  figure,  the  latter  being  fitted  with  bearing  surfaces  for 
connecting  with  the  bars  of  the  link,  and  permitting  sliding  mo- 
tion between  the  two. 

The  pin  is  connected  with  the  lower  end  of  the  valve  stem, 
which  is  formed  in  the  usual  manner  with  brasses  and  cap.  See 
also  Fig.  248.  The  valve  stem  is  usually  guided  by  means  of  a 
special  guide  or  bearing  as  shown  in  Figs.  100,  247,  which  sup- 
ports it  against  side  stress,  especially  at  the  stuffing-box  just 
above.  In  good  practice  the  valve-rod  stuffing-box  is  usually 
packed  with  some  form  of  metallic  packing,  and  is  of  the  same 


VALVES  AND  VALVE  GEARS. 


403 


general  form  and  arrangement  as  the  piston-rod  stuffing-box 
described  in  Sec.  24  [7].  Passing  through  the  stuffing-box  the 
valve-stem  is  attached  to  the  valve,  and  thus  the  chain  of  con- 
nections between  the  excentric  and  the  valve  is  completed. 

The  assemblage  of  these  various  parts  of  a  Stephenson 
valve  gear  is  further  illustrated  in  Fig.  247,  showing  the  upper 
ends  of  the  excentric  rods,  the  link,  link  block,  valve-sttm  and 
guide,  bridle  rods,  rock-shaft  arm  and  brackets  for  supporting 
the  shaft,  and  independent  cut  off  control  in  rock-shaft  arm. 


Marine  Engineering 


Fig.  247.     Arrangement    of   Stephenson    Link   and    Rock    Shaft    Connections. 

Reference  should  also  be  made  to  Figs.  97,  99,  100  for  further 
general  illustrations  of  this  gear. 

When  two  piston  valves  are  driven  side  by  side  as  is  very 
commonly  the  case  on  the  L.  P.  or  I.  P.  cylinders,  the  two  valve- 
stems  are  connected  across  by  a  yoke  as  shown  in  Fig.  248, 
which  in  turn  is  connected  to  the  link  block  by  a  form  of  bearing 
similar  to  that  for  the  single  stem.  In  such  case  the  guide  is 
very  commonly  attached  tp  the  yoke,  the  arrangement  consist- 


404 


PRACTICAL  MARINE  ENGINEERING. 


ing  of  a  dovetailed  or  gibbed  slide  and  guide,  the  first  formed  on 
the  yoke,  and  the  second  by  a  vertical  plate  or  bar  projecting 


SCALE  OF  FEET 


Vi       #         0  1  2  3  4  5 

Fig.  248.    Yoke   and   Guide   for   Driving   Double   Piston   Valves. 

downward  from  the  bottom  of  the  cylinder  head  as  shown  in 
the  figure. 


VALVES  AND   VALVE  GEARS. 


405 


Sec.  54-  VAI,VE  SETTING. 

[i]    Putting  an  Engine  on  the  Center. 

One  of  the  important  features  of  valve  setting  is  the  placing 
of  the  engine  on  the  centers  or  dead-points  in  order  to  deter- 
mine the  lead.  In  a  rough  way  this  may  be  done  by  turning  the 
engine  and  watching  the  cross-head  slide  as  it  approaches  the 
dead-points.  The  slide  will  move  along  the  guide,  more  and  more 
slowly,  and  will  finally  stop  and  begin  to  return.  Just  as  the  far- 
thest point  is  reached,  the  crank  is  on  the  dead-point.  By  mov- 
ing the  engine  back  and  forth  and  watching  carefully  the  move- 
ment of  the  slide  relative  to  a  light  mark  or  score  on  the  guide, 
the  desired  point  may  be  determined  with  fair  accuracy  for  pur- 
poses of  valve  setting. 

The  difficulty  in  making  an  accurate  determination  by  this 
method  lies  in  the  fact  that  when  near  the  center  the  crank  mav 


Marine  Engi 


Fig.  249.     Putting  an  Engine  on  the  Center. 

be  moved  to  and  fro  through  a  sensible  angle  with  hardly  a  no- 
ticeable movement  of  the  slide.  Hence  while  it  is  possible  to 
determine  to  a  nicety  the  point  on  the  slide  which  corresponds 
to  the  highest  or  lowest  position  of  the  piston,  it  is  less  easy 
to  know  just  where  to  set  the  crank  so  as  to  have  it  accurately 
correspond  to  the  same  location.  For  more  accurate  setting  the 
following  method  may  be  used. 

The  engine  is  placed  with  the  cross-head  slide  at  a  sma'll 
distance  from  the  lowest  or  highest  position.  A  mark  A  is  then 
made  on  the  slide  and  "a  corresponding  mark  B  on  the  guide. 
The  distance  which  the  cross-head  should  be  placed  from  the 
center  when  these  marks  are  made  depends  of  course  on  the 
size  of  the  engine,  but  I  or  2  inches  or  say  1-20  to  i-io  the  stroke 


4o6  PRACTICAL  MARINE  ENGINEERING. 

will  be  a  suitable  distance.  See  Fig.  249.  Another  pair  of 
marks  P,  Q,  is  next  made  on  the  forward  end  of  the  shaft  and 
the  adjacent  brass,  or  on  one  of  the  coupling  flanges  and  an  ad- 
jacent block  or  bar  set  up  for  the  purpose.  The  object  is  sim- 
ply to  have  two  pairs  of  marks,  one  on  the  cross-head  slide  and 
its  guide,  and  one  on  the  shaft  and  its  support  or  guide  or  an  ad- 
jacent and  fixed  object.  The  engine  is  then  moved  around  con- 
tinuously in  one  direction  past  the  center  till  the  cross-head  slide 
moves  back  and  the  mark  A  again  comes  opposite  B.  The 
point  P  on  the  shaft  in  the  meantime  will  have  moved  on  to  a 
new  location,  and  a  corresponding  mark  R  is  made  on  the  bear- 
ing or  stationary  part  of  the  engine  on  which  the  first  mark  Q 
was  placed.  The  angle  between  these  two  marks  Q  R,  on  the 
shaft  or  coupling  corresponds  to  the  movement  of  the  cross-head 
from  the  position  of  the  first  pair  on  to  the  end  of  the  stroke  and 
back  again  an  equal  distance.  A  mark  S  midway  between  Q 
and  R,  will  give  the  proper  location  for  the  mark  P  when  the 
cross-head  is  at  the  end  of  the  stroke  and  the  crank  on  its  dead 
point.  In  this  way  by  moving  the  shaft  till  P  is  brought  oppo- 
site S  the  location  of  the  crank  for  each  dead  point  may  be  quite 
accurately  found. 

[2]  Setting  the  Valve. 

To  return  to  the  setting  of  the  valve  we  first  note  that  the 
distribution  of  the  steam  to  a  cylinder  by  means  of  a  slide  valve 
depends  on  four  chief  items  : 

(1)  The  throw  of  the  excentric. 

(2)  The  angular  location  of  the  excentric  relative  to  the 
crank. 

(3)  The  length  of  the  valve  stem. 

(4)  The  steam  and  exhaust  laps. 

Now  let  us  assume  that  the  parts  of  the  valve  gear  are  made, 
and  that  it  simply  remains  to  connect  them  up  and  make  the 
proper  adjustments.  It  is  seen  that  we  have  but  two  items 
which  may  be  varied,  or  which  may  enter  into  the  question  of  the 
setting  of  the  valve.  These  are  (2)  and  (3)  above.  We  should 
first  adjust  for  (3)  and  then  for  (2). 

Referring  to  Sec.  55  [2]  (9)  it  appears  that  an  incorrect 
length  of  valve-rod  will  give  an  improper  balancing  up  of  the 
events  for  the  top  and  bottom  of  the  cylinder.  Hence  the  vari- 


VALVES  AND   VALVE  GEARS.  407 

ous  events  for  both  ends  must  be  examined  and  compared.  To 
this  end  the  entire  gear  is  connected  up  according  to  judgment, 
the  link  being  placed  in  the  position  intended  for  normal  running 
ahead,  and  the  necessary  arrangements  made  for  observing  the 
movement  of  the  valve.  If  the  valve  is  a  flat  slide  the  valve 
chest  cover  is  left  off  for  this  purpose.  With  piston  valves, 
however,  it  is  necessary  to  observe  the  movement  of  the  valve  by 
means  of  peep  holes  through  the  shell  of  the  chest,  such  holes 
being  fitted  with  screw  plugs  or  covered  by  caps  when  the  en- 
gine is  closed  up  and  ready  for  operation.  In  this  manner  the 
lead  is  observed  while  the  engine  is  on  fHe  centers,  and  the 
points  of  cut-off  and  other  items  are  observed  for  each  end  of  the 
cylinder.  The  location  of  the  valve  on  the  stem  is  then  varied 
until  a  fair  balance  between  the  two  ends  is  obtained.  It  will  be 
found  that  with  anything  like  equal  leads  the  cut-off  will  be  later 
on  the  down  than  on  the  up  stroke,  or  with  an  attempt  to  even 
the  points  of  cut-off  the  lead  and  port  opening  on  top  will  be- 
come too  small  and  the  lead  on  the  bottom  excessive.  It  will 
often  be  found  that  with  something  approaching  equal  leads  on 
top  and  bottom,  the  points  of  cut-off  will  vary  in  the  two  ends 
by  nearly  or  quite  10  per  cent,  or  even  more. 

It  is  readily  seen  that  similar  derangements  will  result  from 
an  attempt  to  balance  the  exhaust  items.  In  general  it  is  far 
better  not  to  attempt  to  exactly  balance  any  one  item  in  the  two 
ends,  but  simply  to  aim  for  the  best  all  around  combination  of 
events  which  can  be  obtained  in  the  given  case. 

When  a  fair  balance  is  thus  obtained,  the  question  of  the  point 
of  average  cut-off,  steam-opening,  release  and  compression  may 
be  taken  up.  Changes  in  these  items  require  a  change  in  the 
angular  location  of  the  excentric  relative  to  the  shaft,  and  it  may 
be  shifted  according  to  the  relations  shown  in  the  table  of  Sec. 
47  [2]  until  the  general  character  of  the  various  items  is  made 
satisfactory. 

It  thus  appears  that  of  the  two  items, length  of  valve-rod  and 
location  of  excentric,  the  latter  really  fixes  the  general  character 
of  the  various  items,  while  the  former  makes  it  possible  to  ap- 
proximately even  up  or  balance  the  various  items  between  the 
two  ends,  according  to  what  seems  the  most  desirable  average 
distribution. 

If  the  excentric  is  shifted  through  any  considerable  an.rle 
from  its  first  location  it  will  be  necessary  to  again  examine  the 


4oS  PRACTICAL  MARINE  ENGINEERING. 

question  of  balance  between  the  two  ends,  and  to  again  adjust 
the  length  of  valve-rod. 

If  by  the  adjustment  of  both  valve-rod  and  excentric,  the 
desired  events,  openings,  etc.,  cannot  be  obtained,  it  means  that 
the  trouble  lies  with  one  or  both  of  the  other  items,  throw  of  ex- 
centric  and  steam  or  exhaust  lap,  and  steps  must  be  taken  to 
modify  these  features  as  the  conditions  may  require. 

The  following  table  gives  an  illustration  of  the  balancing  up 
of  the  various  items  in  the  two  ends  of  the  cylinder. 

TOP.  BOTTOM. 


Steam  opening 

.7  per  cent,  before 
end  of  stroke 

.4  per  cent,  before 
end  of  stroke 

Steam  closure  or  cut-off 

68  per  cent. 

59  per  cent. 

Exhaust  opening 

90  per  cent. 

91  per  cent. 

Exhaust  closure 

85  per  cent. 

84  per  cent. 

Steam  lap 

2.44  in. 

2.40  in. 

Exhaust  lap 

—  .12  in. 

+  .68  in. 

Steam  lead 

.60  in. 

.52  in. 

Port  opening  for  steam 

2.08  in. 

2.12  in. 

Angle  of  advance 

33  degrees 

Throw  of  excentric> 

4  15-16  in. 

The  setting  of  the  valve  may  of  course  be  examined  or  re- 
adjusted at  any  time,  as  desired,  by  the  use  of  the  same  general 
method. 

[3]  Valve  Setting  from  the  Indicator  Card. 

The  indicator  cards  interpreted  in  accordance  with  the  re- 
lations given  below  in  Sec.  55  [2]  furnish  most  valuable  evidence 
as  to  the  adjustment  of  the  valve  gear,  and  its  suitability  for 
operation  under  steam.  In  attempting  a  readjustment  or  re- 
setting by  the  aid  of  the  indications  given  by  the  cards,  the 
question  of  balance  between  the  two  ends  as  affected  by  the 
length  of  valve-rod  should  be  taken  first,  next  the  items  depend- 
ing on  the  angular  location  of  the  excentric,  and  last  the  ques- 
tion of  lap  and  excentric  throw. 

If  the  cards  are  pushed  over  to  one  side  or  show  differences 
in  the  two  ends  as  in  Fig.  260  it  is  evidence  that  the  valve  stem  is 
not  of  the  right  length,  and  it  must  be  changed  accordingly. 


VALVES  AND   VALVE  GEARS.  409 

This  is  done  first,  cards  being  taken  after  each  change  until 
the  two  ends  are  fairly  well  balanced  up.  Attention  is  next 
given  to  the  location  of  the  excentric.  The  points  of  cut-off,  re- 
lease and  compression  will  show  whether  the  angular  advance  is 
too  large  or  too  small,  and  the  readjustment  is  made  accordingly. 
A  change  in  the  angle  of  the  excentric  for  the  purpose  of  adjust- 
ing any  one  item  is  moreover  liable  to  disturb  other  items  in 
such  way  as  to  require  a  readjustment  of  the  lap,  and  is  there- 
fore to  be  avoided  unless  considered  necessary.  Thus  if  the 
cut-off  is  too  late,  for  example,  and  the  excentric  is  turned  so  as 
to  increase  the  angular  advance,  the  cut-off  will  be  made 
earlier  and  the  exhaust  and  compression  as  well,  while  the 
lead  will  be  increased.  If  the  change  necessary  to  adjust  the 
cut-off  produces  too  great  a  disturbance  in  the  exhaust  and  com- 
pression, or  if  in  general  a  suitable  and  satisfactory  arrange- 
ment of  events  cannot  be  reached  by  adjustment  of  the  excentric 
and  valve  rod  only,  it  means  that  the  lap  is  at  fault  or  perhaps 
the  throw  of  excentric.  Change  in  the  lap  can  of  course,  only 
be  effected  by  removing  the  valves  and  cutting  them  down  if  it 
is  to  be  decreased,  or  fitting  a  new  valve  or  head  if  it  is  to  be 
increased.  Similarly  change  in  the  throw  of  the  excentric  can 
only  be  effected  by  a  removal  of  the  old  and  fitting  a  new  one 
of  proper  throw. 


4io 


PRACTICAL  MARINE  ENGINEERING. 


CHAPTER  VIII. 

STEAM   ENGINE  INDICATORS  AND   INDICATOR  CARDS. 

Sec.  55-  INDICATOR  CARDS. 

[i]  Descriptive. 

An  indicator  card  is  a  diagram  showing  for  each  point  of 
the  stroke  in  both  directions  the  steam  pressure  on  the  piston. 
Thus  Fig.  250  represents  an  indicator  card  showing  the  steam 
pressure  above  the  piston,  say,  for  both  the  down  and  up 
strokes.  RS  is  the  line  of  zero  pressure  from  which  all  pressures 
are  measured  upward  according  to  the  scale  of  the  diagram. 
This  is  called  the  absolute  pressure  line.  A  is  the  beginning  oi 
the  down  stroke,  B  the  point  of  cut-off,  C  the  point  of  exhaust 


Fig.  250.     Indicator    Card. 

opening,  and  D  the  end  of  the  stroke.  The  line  AB  is  called  the 
steam  line  and  shows  the  steam  pressure  on  the  upper  side  of  the 
piston  from  the  beginning  of  the  stroke  to  cut-off.  The  line  BC 
is  called  the  expansion  line  and  shows  the  decreasing  values  of 
the  pressure  during  that  part  of  the  stroke.  At  C  the  exhaust 
opens  and  the  pressure  drops  suddenly  as  shown  by  CD.  For  the 
return  or  up  stroke,  D  is  the  beginning,  E  the  point  of  exhaust 
closure  or  beginning  of  compression  above  the  piston,  and  F  the 


INDICATORS   AND   INDICATOR    CARDS.  4'i 

point  of  steam  opening  just  before  the  beginning  of  the  next 
down  stroke.  CDE  is  the  exhaust  line  and  shows  the  nearly  con- 
stant pressure  during  this  period.  EF  is  the  compression  line 
and  shows  the  increasing  pressures  on  the  return  stroke  after  the 
closure  of  the  exhaust  valve.  FA  is  the  admission  line  and 
shows  the  sharp  jump  upward  as  the  steam  is  opened  again  just 
before  the  beginning  of  the  next  down  stroke.  The  line  PQ 
drawn  when  the  space  below  the  indicator  piston  is  shut  off 
from  the  engine  cylinder  and  connected  to  the  air  is  called  the 
atmospheric  line.  The  distance  PR  between  RS  and  PQ  thus 
represents  the  pressure  of  the  atmosphere,  14.7  pounds  per 
square  inch,  its  length  depending  of  course  on  the  scale  of  the 
diagram.  Thus  for  the  down  stroke  the  varying  pressures  on 
the  top  of  the  piston  are  shown  by  the  varying  distances  from 
RS  to  ABCD,  while  for  the  up  stroke  the  pressures  on  the 


Fig.  251.     Pair  of  Indicator  Cards. 

same  side  of  the  piston  are  shown  by  the  distances  from  RS  to 
DEFA. 

There  will  be,  of  course,  a  similar  diagram  for  .the  head  end 
of  the  cylinder  showing  the  pressures  below  the  piston  for  both 
the  up  and  down  strokes  in  the  same  manner  as  for  the  diagram 
described.  Such  a  pair  of  diagrams  taken  from  actual  practice 
is  shown  in  Fig.  251. 

Let  us  now  compare  the  cards  of  Figs. 250, 251  with  Fig.  252, 
the  latter  showing  a  so-called  ideal  card ;  that  is,  a  card  which 
would  be  given  if  the  valves  opened  and  closed  instantaneously, 
if  when  closed  they  were  tight  against  all  leakage,  if  there  were 
no  loss  of  pressure  due  to  friction  of  steam  in  the  passage,  and 
if  the  expansion  and  compression  lines  were  equilateral  hyper- 
bolas. Instead  of  these  conditions  the  valves  open  and  close 
gradually,  even  when  closed  there  may  be  some  leakage,  there 
is  always  some  loss  of  pressure  due  to  friction  or  resistance  to 
the  flow  of  steam,  especially  through  a  gradually  closing  or 


412  PRACTICAL  MARINE  ENGINEERING. 

opening  port  and  the  expansion  and  compression  lines  are  not 
true  hyperbolas.  Added  to  these  we  have  the  inertia  of  the  indi- 
cator piston  which  prevents  it  from  following  with  absolute  ex- 
actness all  the  variations  of  pressure  as  they  occur. 

As  a  result  of  these  various  causes  the  actual  engine  and  in- 
dicator give  us  the  diagrams  of  Figs.  250  and  251  rather  than 
such  as  Fig.  252.  The  gradual  opening  and  closure  of  the  valve 
rounds  off  the  various  corners,  while  the  steam  line  instead  of 
being  horizontal,  droops  somewhat,  due  to  the  loss  of  pressure 
through  the  ports  and  passages.  The  piston,  of  course,  moves 
faster  as  it  approaches  mid-stroke  and  hence  the  steam  must 
flow  in  at  an  increasing  velocity  to  fill  up  the  space  behind  the 
advancing  piston.  The  higher  the  velocity  the  greater  the  loss 
of  pressure,  and  hence  there  is  a  continual  slope  down  from  the 
beginning  of  the  stroke  as  shown  in  Fig.  251  and  often  to  a  far 


Fig.  252.    Ideal  Indicator  Card. 

more  pronounced  degree.  The  actual  point  of  cut-off  is  also 
not  always  easy  to  locate,  rounded  off  as  it  is  by  the  gradual 
closure  of  the  valve.  We  may,  however,  properly  consider  that 
the  point  of  actual  final  closure  is  where  the  curve  changes  di- 
rection of  curvature,  that  is,  from  convex  to  concave,  as  at  or 
near  P.  Fig.  251.  It  is  sometimes  considered  that  the  point  of 
equivalent  cut-off  is  more  nearly  obtained  by  continuing  the 
curve  back  as  shown  by  the  dotted  line  to  Q  and  supposing 
a  sharp  cut-off  at  this  point.  The  result  would  then  be  an  ex- 
pansion line  from  Q  similar  to  that  which  is  obtained  by  the 
gradual  closure  in  the  actual  case. 

The  steam  engine  indicator  diagram  is  valuable  for  two 
chief  purposes. 

(a)  It  enables  us  to  judge  of  the  operation  of  the  valve  by 
noting  the  various  events,  steam  opening  and  closure,  the  loca- 


INDICATORS   AND   INDICATOR   CARDS.  413 

tion  relative  to  that  of  the  piston,  the  resulting  piston  pressure, 
and  to  answer  various  questions  relative  to  the  general  problem 
of  the  distribution  of  steam  to  the  cylinder. 

(b)  It  enables  us  to  answer  all  questions  which  depend  on 
the  amount  and  distribution  of  steam  pressure  on  the  piston  and 
thus  to  determine  the  mean  pressure,  and  knowing  the  revolu- 
tions to  find  the  indicated  horse  power;  also  the  turning  effort 
at  the  various  points  of  the  revolution,  and  the  mean  effort  for 
the  entire  revolution. 

[a]  The  Indicator  Card  and  the  Operation  of  the  Valve  Gear. 
We  will  now  consider  briefly  the  more  important  derange- 
ments which  may  be  met  with  in  the  valve  gear,  and  the  re- 
sults as  shown  by  the  indicator  card. 


Fig.  253.     Indicator   Cards   with   Angular   Advance   too   large. 

(i)  E.vcentric  too  far  from  a  line  at  right  angles  to  the  crank ; 
that  is,  angular  advance  d  too  large  (Sec.  47  [i]). 

Results:  Cut-off  too  early,  steam-lead  large,  exhaust  open- 
ing and  closure  early.  In  short,  the  whole  round  of  events  is 
ahead  of  time.  See  Fig.  253. 


Fig.  254.     Indicator    Card    with   Angular   Advance   too    small. 

(2)  E.vcentric  too  near  a  line  at  right  angles  to  the  crank ; 
that  is,  angular  advance  d  too  small  (Sec.  47  [i]). 

Results:  Cut-off  late,  steam  lead  small  or  even  negative, 
compression  small,  steam  opening  late,  exhaust  opening  and 
closure  late.  In  short,  the  whole  round  of  events  is  behind  time. 
See  Fig.  254. 


4i4  PRACTICAL  MARINE  ENGINEERING. 

(3)  Steam  lap  too  large. 

Results:  Cut-off  early,  steam  opening  late  and  lead  small  or 
even  negative,  port  opening  small  with  a  probable  wire  draw- 
ing of  the  steam,  and  drop  of  pressure  on  steam  line.  See  Fig. 

255- 


Fig.  255.     Indicator  Card  with  Steam  Lao  too  large. 


Fig.  256.     Indicator  Card  with  Steam  Lap  too  small. 

(4)  Steam  lap  too  small. 

Results:  Cut-off  late,  steam  opening  early  and  lead  large, 
port  opening  large.     See  Fig.  256. 

(5)  Exhaust  lap  too  large. 

Results:  Exhaust  closure  early  and  compression  large,  ex- 
haust opening  late  and  exhaust  lead  small.     See  Fig.  257. 


Fig.  257.     Indicator    Card   with    Exhaust    Lap   too   large. 


Fig.  258.     Indicator    Card   with   Exhaust   Lap   too   small. 

(6)  Exhaust  lap  too  small. 

Results:  Exhaust  closure  late  and  compression  small,  ex- 
haust opening  early.     See  Fig.  258. 


INDICATORS   AND   INDICATOR    CARDS.  4«5 

(7)  Compression  excessive. 

Results:  The  pressure  in  the  cylinder  may  be  carried  above 
that  in  the  valve  chest  before  the  steam  valve  opens,  thus  form- 
ing a  loop  as  shown  in  Fig.  253.  This  may  be  due  to  either  (i) 
or  (5)  above. 

(8)  Expansion  Excessive. 

Results:  The  pressure  in  the  cylinder  may  fall  below  that 
in  the  next  receiver  or  exhaust  space  beyond,  thus  forming  a 
loop  as  shown  in  Fig.  259. 


Fig.  259.     Indicator  Card  with  Excessive  Expansion. 

(9)   Valve  Stem  too  long. 

Results:  This  means  that  the  middle  of  the  stroke  of  the 
valve  is  placed  too  high  relative  to  the  ports.  The  results  for 
an  outside  valve  will  be  to  give  too  much  steam-lap  on  top  and 
exhaust  lap  on  the  bottom,  and  too  little  steam  lap  on  the  bot- 
tom and  exhaust  lap  on  top.  Hence  we  shall  have  : 

Steam  opening  in  top  late  and  small  and  cut  off  early. 

Steam  opening  on  bottom  early  and  full,  and  cut  off  late. 

Exhaust  opening  on  top  early  and  full  and  closure  late. 

Exhaust  opening  on  bottom  late  and  small  and  closure 
early.  See  Fig.  260. 


Fig.  260.     Indicator  Card  with  Valve  Stem  too  long  or  too  short. 

(10)  Valve  Stem  too  short. 

Results:  Similar  to  those  for  (9)  but  oppositely  related  to 
the  ends  of  the  cylinder. 


416  PRACTICAL  MARINE  ENGINEERING. 

To  these  we  may  also  add  the  following. 

(n)  Leaky  piston  or  piston  rod  stuffing-box. 

Results:  The  expansion  line  will  be  steeper  than  it  should  be. 
The  compression  line  may  also  flatten  off  somewhat  near  the 
top. 

(12)  Port  openings  or  Passages  too  small. 

Results:  Wire  drawing  or  loss  of  pressure  on  the  steam  line 
and  rise  of  pressure  on  the  exhaust  line.  See  Figs.  251,  255. 

It  will  be  noted  in  the  above  that  different  causes  may  pro- 
duce similar  results,  so  that  in  interpreting  a  given  set  of  cards 
caution  must  be  used  in  working  back  from  result  to  probable 
cause  and  remedy.  This  operation  may  be  aided  by  the  follow- 
ing general  hints. 

It  will  be  noted  that  the  general  effect  of  a  valve-stem  too 
long  or  too  short  is  to  effect  the  two  ends  of  the  cylinder  in  op- 


Fig.  261.     Indicator  Card  Showing  Combination  Effect. 

posite  directions,  thus  giving  the  cards  the  appearance  of  hav- 
ing been  pushed  over  in  one  direction  or  the  other  as  in  Fig.  260. 
On  the  other  hand,  if  the  valve-stem  is  of  proper  length  but  the 
excentric  is-  improperly  set  the  results  will  be  of  the  same  kind  in 
both  ends  of  the  cylinder  as  shown  in  Fig.  253.  Various  com- 
binations of  these  may  exist  in  the  same  engine.  Thus  a  pair 
of  cards  as  shown  in  Fig.  261  indicates  an  incorrect  length 
of  valve-stem,  an  incorrect  adjustment  of  the  laps,  with  perhaps 
too  large  an  angular  advance.  The  combination  nearly  corrects 
certain  difficulties  and  makes  others  still  worse. 

Various  special  features  may  combine  to  make  the  so-called 
"freak"  cards,  but  we  shall  not  examine  this  part  of  the  subject 
further  as  such  freaks  are  of  rare  occurrence,  and  a  careful  study 
of  the  results  of  the  various  single  derangements  as  given  above 
in  (i)  to  (12)  will  usually  be  sufficient  to  show  the  nature  of  the 
trouble. 


INDICATORS   AND   INDICATOR    CARDS.  4»7 

[3]  Working  Up  Indicator  Cards  for  Power. 
From  the  principles  of  mechanics  we  know  that  work  is  the 
result  of  a  force  or  effort  acting  through  a  distance,  and  is 
measured  by  the  product  of  the  force  in  pounds  by  the  distance 
in  feet.  This  gives  the  measure  of  the  work  in  foot-pounds. 
Power  measures  the  capacity  to  perform  a  certain  amount  of 
work  in  a  given  time.  The  common  unit  is  the  horse  power, 
which  is  33,000  foot-pounds  of  work  done  in  one  minute  of  time. 
Hence  to  find  the  power  of  an  engine  we  have  two  chief  steps : 

(1)  To  find  the  foot-pounds  of  work  done  per  minute. 

(2)  To  reduce  this  to  horse  power  by  dividing  by  33,000. 

It  may  be  noted  here  that  the  term  Indicated  Horse  Power 
means  simply  the  horse  power  as:  determined  from  the  indicator 
cards. 

Now  by  definition  the  foot  pounds  per  minute  for  the  steam 
engine  will  be  the  product  of  the  acting  force  multiplied  by 
the  distance  through  which  it  acts  in  one  minute.  The  acting 
force  equals  the  mean  load  on  the  piston,  and  this  equals  th^ 
mean  effective  pressure  per  square  inch  multiplied  by  the  area 
in  square  inches.  The  distance  acted  through  per  minute  must 
be  measured  in  feet,  and  equals  twice  the  stroke  multiplied  by 
the  number  of  revolutions  per  minute. 

Let  p  =  mean  effective  pressure  in  pounds  per  square  inch ; 
A  =  area  of  piston  in  square  inches ;  L  =  length  of  stroke  in 
feet ;  N  =  revolutions  per  minute.  Then  pA  —  acting  force  or 
mean  total  load  on  the  piston  measured  in  pounds,  and  2LN  — 
distance  moved  per  minute  in  feet  =  piston  speed.  Hence 
foot-pounds  of  work  per  minute  equals  product  (pA)  X  (2LN) 
or  what  is  the  same  thing  2pLAN.  Hence  we  have  the  formula : 

2  pLAN 
Horse  power  =    -±— 

33000 

This  is  the  usual  formula  for  finding  the  indicated  horse 
power,  and  is  commonly  employed  for  working  up  indicator 
cards  for  this  purpose. 

The  reasons  for  measuring  L  in  feet  and  A  in  square  inches 
will  be  readily  seen  from  the  following  considerations.  Work 
is  composed  of  two  factors,  the  force  factor  and  the  distance 
factor.  The  first  must  be  measured  in  pounds  and  the  second 
in  feet.  The  product  pA  is  the  force  factor,  and  since  /»  is 
usually  measured  in  pounds  per  square  inch,  A  must  be  measured 


4i8  PRACTICAL  MARINE  ENGINEERING. 

in  square  inches  in  order  that  pA  may  be  the  total  mean  load 
in  pounds.  The  product  2LN  is  the  distance  factor,  and  hence 
2.L  the  distance  traveled  per  revolution  must  be  measured  in 
feet,  in  order  that  2.LN  may  be  the  distance  traveled  per  minute 
measured  in  feet.  The  product  (pA)  X  (2ZJV)  or  2pLAN  will 
then  give  the  work  measured  in  foot-pounds  as  we  have  seen 
above. 

We  will  now  give  by  rule  the  operations  necessary  to  find 
the  indicated  horse  power,  as  expressed  by  the  formula  above. 

Rule — Multiply  together  the  mean  effective  pressure  in 
pounds  per  square  inch  by  the  length  of  the  stroke  in  feet, 
and  this  product  by  the  area  of  the  piston  in  square  inches,  anrl 
this  product  by  the  number  of  revolutions  per  minute,  and  this 
product  by  2,  and  then  divide  the  final  product  by  33,000.  The 
quotient  will  give  the  indicated  horse  power. 


Fig.  262.     Mean   Effective   Pressure   from   Indicator   Card. 

Now  the  various  factors  which  enter  into  either  the  formula 
or  rule  for  horse  power,  the  length  of  stroke  and  area  of  the 
piston  come  from  the  dimensions  of  the  engine,  and  the  revolu- 
tions per  minute  from  the  counter,  or  by  actually  counting  them, 
watch  in  hand.  There  remains  the  mean  effective  pressure  p 
which  must  be  found  from  the  indicator  cards,  and  to  this  part 
of  the  operation  we  now  turn. 

The  mean  pressure  for  a  single  card  such  as  Fig.  262  gives 
simply  the  mean  of  the  pressure  in  one  end  of  the  cylinder,  say 
the  top.  To  obtain  this  mean  pressure  we  may  proceed  in  a 
number  of  different  ways.  Fundamentally  the  mean  of  such  a 
series  of  pressures  as  given  by  the  indicator  card,  is  found  by 
dividing  the  area  of  the  card  by  the  length.  This  gives  the 
side  of  a  rectangle  which  would  have  the  same  area  as 
the  card.  Thus  in  Fig.  262  if  the  rectangle  ABCD  has  the 
same  area  as  the  card,  then  the  side  A  D  of  the  rectangle 
is  the.  mean  height  of  the  card,  and  to  the  proper  scale 


INDICATORS   AND   INDICATOR    CARDS. 


419 


will  give  the  mean  pressure  desired.  Hence  any  method 
which  will  give  the  area  of  the  card  may  be  used  for 
rinding  a  mean  height,  and  hence  a  mean  pressure.  In 
Part  II.,  Sec.  9  [15]  are  given  various  rules  and  methods  for 
finding  the  measure  of  an  irregular  area,  illustrated  by  the  ex- 
ample of  an  indicator  card,  and  any  of  these  may  be  used  as 
there  explained.  The  method  most  commonly  used  is  to  meas- 
ure the  ordinates  on  the  dotted  lines  as  in  the  figure  there  shown, 
take  their  sum,  and  divide  by  their  number,  10.  This  multiplied 
by  the  scale  of  the  indicator  spring  will  give  the  mean  pressure 
desired.  The  simplest  method  of  locating  the  intervals  for  these 
dotted  ordinates  is  that  explained  in  Part  II.,  Sec.  10  [4].  To 
carry  this  out  we  proceed  as  follows  : 

Let  the  card  be  represented  in  Fig.  263,  then  draw  the  lines  at 
the  ends  as  shown,  perpendicular  to  the  atmospheric  line  OA 


Fig.  263.     Subdivision  of  Indicator  Card  for  Obtaining  Mean  Ordinate. 

and  tangent  to  the  card,  thus  fixing  its  length.  Then  lay  off 
the  line  OB  at  an  angle  and  on  OB  lay  off  first  a  half  divi- 
sion Oi,  then  nine  whole  divisions,  and  then  a  half  division  as 
shown.  The  divisions  may  be  taken  from  y±  to  y2  inch  in  ac- 
cordance with  the  length  of  the  card.  Then  drawing  a  line 
from  B  to  A  and  other  parallel  lines  from  the  points  of  division 
on  OB  to  OA,  the  locations  for  the  ordinates  are  determined, 
and  they  may  be  drawn  as  shown.  Where  a  large  number  of 
cards  are  to  be  worked  up  in  this  way,  time  will  be  saved  by 
the  use  of  a  form  of  template  or  pattern  for  locating  these  points. 
Such  an  implement  is  shown  in  Fig.  264  and  consists  of  a  piece 
of  hard  wood  with  small  steel  points  set  in  to  the  edge,  spaced 
according  to  the  lay  out  of  points  along  OB  Fig.  263.  The 
distance  between  the  extreme  points  is  somewhat  greater  than 
the  length  of  the  longest  card  likely  to  be  met  with.  Instead  of 


420 


PRACTICAL  MARINE  ENGINEERING. 


steel  points  set  in  a  block  of  wood,  a  thin  plate  of  steel  may  be 
cut  out  and  filed  up  so  as  to  leave  the  points  projecting  at  the 
desired  intervals.  In  using  this  device  it  is  simply  necessary  to 
draw  lines  tangent  to  the  ends  of  the  card  as  shown,  and  then 
to  place  one  end  of  the  template  on  one  boundary  line  PR  at 
any  convenient  point  as  P,  and  swing  it  to  such  an  angle  as 
will  just  bring  the  other  end  Q  to  the  other  line  QS.  The 
template  is  then  pressed  down  so  as  to  mark  the  paper  with  the 
points,  and  lines  parallel  to  those  at  the  ends  are  drawn  through 
the  points  thus  marked,  as  shown  by  the  lines  of  the  figure. 
In  this  way  the  ordinates  spaced  in  the  manner  desired  may  be 
rapidly  laid  out  and  drawn  in. 

For  summing  the  ordinates  the  method  by  the  use  of  a  strip 
of  paper  as  explained  in  Part  II.,  Sec.  9  [15]   may  be  recom- 


\ 


i    i 


Fig.  264.     Subdivision    of    Indicator    Card    for    Obtaining    Mean   Ordinate. 

mended  as  the  simplest,  quickest  and  most  satisfactory  available 
for  the  purpose. 

Having  thus  in  one  way  or  another  found  the  mean  effective 
pressure  for  one  card,  the  other  one  of  the  pair  is  taken  in  like 
manner,  thus  giving  tlie  mean  effective  for  the  other  end  of  the 
cylinder  or  other  stroke.  These  two  values  may  then  be 
averaged,  and  the  result  taken  as  the  mean  effective  pressure 
for  the  revolution,  thus  furnishing  the  final  factor  p  required  in 
the  formula  or  rule  for  horse  power. 

It  must  be  noted  that  this  operation  is  slightly  in  error  by 
reason  of  the  difference  in  area  between  the  upper  and  lower 
sides  of  the  piston.  On  the  upper  side  the  entire  area  is  effective 


INDICATORS   AND   INDICATOR   CARDS.  4*' 

while  on  the  lower  side  the  piston  rod  takes  out  a  small  area  in 
the  center.  To  take  account  of  this,  we  may  compute  the  I.H.P. 
for  each  end  of  the  cylinder  separately.  To  this  end  we  take 
each  card  by  itself,  say  the  head  end  first,  and  find  the  mean. 
effective  pressure  which  we  may  denote  by  /x.  Let  the  entire 
piston  area  he  Al.  Then  as  before  the  mean  load  or  average 
acting  force  is  the  product  of  the  two,  />,  Ar  The  distance  acted 
through  is  L  for  each  down  stroke,  and  the  number  of  down 
strokes  per  minute  is  equal  to  the  number  of  revolutions  Ar. 
Hence  the  distance  per  minute  for  the  down  strokes  is  LN  and 
the  I.H.P.  for  this  end  of  the  cylinder  will  be: 


i 

33000  33000 

In  a  similar  manner  we  then  find  the  mean  effective  pres- 
sure for  the  bottom  or  crank  end  of  the  cylinder  which  we  may 
call  pi.  Then  taking  from  Ai  the  area  of  the  piston  rod,  we  have 
the  effective  area  of  the  bottom  of  the  piston  which  we  may 
call  At.  Then  similarly  as  in  the  head  end  we  have  for  the 
I.H.P.  in  the  crank  end, 

H   ---  P*A    LX  ^P~-LA-N 

33000  33030 

The  total  I.H.P.  will  then  be  the  sum  of  these  for  the  two 
strokes  up  and  down,  or  : 

IH.P.  ^  H,-\   H,= 

For  illustration  see  example  (7)  below. 

Mean  Effective  Pressure  by  the  Aid  of  the  Planimctcr. 

The  planimeter,  an  instrument  for  measuring  areas,  is  also 
frequently  used  for  working  up  indicator  cards,  and  where  the 
number  is  large  will  be  found  of  great  service.  Such  instru- 
ments may  be.  obtained  of  most  makers  of  indicators  or  of 
dealers  in  mathematical  instruments.  General  directions  for 
their  use  will  accompany  them.  The  following  hints  may  be 
given  for  their  use  with  indicator  cards. 

Where  the  instrument  has  an  adjustable  bar  it  should  be 
sel  so  ns  to  read  the  area  in  square  inches.  \Yhere  the  bar  is 
not  adjustable  the  instrument  is  usually  already  set  to  read  in 
terms  of  this  unit.-  The  order  of  procedure  is  then  as  follows  : 

(i)  Draw  lines  at  the  ends  of  the  card  at  right  angles  to 
the  atmospheric  line  so  as  to  be  able  to  determine  its  length. 


422  PRACTICAL  MARINE  ENGINEERING. 

(2)  Place  the  instrument  and  card  in  a  suitable  position, 
and  read  the  record  wheel,  putting  down  the  result,  say  3.26  as 
below : 

Readings.     Differences.     Average. 

First   3.26 

Second   7.08  3.82 

Third    10.92  3.84  3.83 

(3)  Then  trace  around  the  contour,  usually  in  the  direction 
with  the  hands  of  a  watch  for  a  second  reading  greater  than  the 
first,  and  come  back  carefully  to  the  starting  point.    Then  read 
again  and  set  down  the  result,  say  7.08  below  the  first  as  shown. 

(4)  Then   repeat,   tracing  around  as  before,   read  and   set 
down  the  result,  say  10.92,  below  the  others  as  shown.    In  mak- 
ing the  last  reading  it  will  be  noted  that  on  the  instrument  itself 
we  might  be  able  to  read  only  0.92,  but  the  increase  upward 
from  3  to  7  shows  that  the  wheel  has  passed  the  starting  point 
and  begun  again,  so  that  we  must  add  the  ten  and  write  10/12. 

(5)  We  then  take  the  difference  of  the  readings,  the  first  from 
the  second  and  the  second  from  the  third  and  set  down  as  shown, 
and  then  average  these  two  numbers,  thus  finding  in  the  present 
case  3.83  for  the  area  in  square  inches.    The  reason  for  going 
around  the  area  twice  is  to  have  two  measurements,  so  that  each 
will  give  a  check  on  the  other.     If  they  differ  widely  an  error 
somewhere  is  certain,  and  they  must  be  repeated,  while  if  nearly 
the  same,  as  in  the  case  given  above,  the  error  is  no  more  than 
must  be  expected  with  such  means,  and  the  average  may  be 
taken  as  the  value  of  the  area  desired. 

(6)  We  next  divide  the  area  by  the  length  of  the  card.    Thus 
suppose  in  the  case  in  hand  that  the  length  is  4.2  inches.    Then 
3.83  -r-  4.2  =  .912  inches.    This  is  the  mean  ordinate  or  mean 
height  of  the  card  in  inches. 

(7)  We  next  multiply  by  the  scale  of  the  indicator  spring 
and  thus  find  the  mean  effective  pressure  desired.     Thus  sup- 
pose the  spring  to  be  60  pounds  to  the  inch.    Then  60  X  .912  = 
54.72  pounds.    This  is  then  the  mean  effective  pressure  for  the 
stroke  as  given  by  the  card  thus  measured. 

We  then  proceed  similarly  with  the  other  card,  and  use  the 
results  for  the  determination  of  horse  power  in  the  manner  al- 
ready explained. 


INDICATORS   AND   INDICATOR    CARDS.  4*3 


Illustrative  Examples. 

(1)  The  area  of  an  indicator  card  is  2.87  sq.  in.  and  its 
length  is  3.8  in.     What  is  the  mean  height? 

Solution:    2.87  -4-  3.8  =  .755  in. 

(2)  The  scale  of  the  indicator  spring  is  40  Ibs.  per  inch. 
What  is  the  m.e.p.l* 

Solution:  .755  X  40  =  30.2  Ibs. 

(3)  The  ordinates  measured  in  inches  taken  from  an  indi- 
cator card  divided  up  as  in  Fig.  263  are  as  follows : 

.91,  1.30,  1.44,  1.40,  1.35,  1.20,  .95,  .80,  .70,  .25,  and  the 
scale  of  the  indicator  spring  is  60  Ibs.  per  inch.  Find  the  m.e.p. 

Solution :  Adding  the  lengths  as  given,  we  have  for  the  sum 
10.40.  Hence  dividing  by  10  we  have  for  the  mean  ordinate 
10.40  -f-  10  —  1.04.  Hence  the  m.c.p.  is  60  X  1.04  =  62.4  Ib. 

(4)  The  total  length  between  marks   on  a  strip  of  paper 
used  to  measure  the  ordinates  as  described  in  Part  II.,  Sec. 
9  [15]  is  found  to  be  6.3  in.     The  scale  of  the  spring  is  20  Ib. 
Find  the  m.c.p. 

Solution:  6.3  -f-  10  =  .63  in.  =  mean  height,  and 
.63  X  20  =  13.6  Ib.  =  m.e.p. 

(5)  Given  an  indicator  card  with  ordinates  spaced  as  in  Fig. 
263.     The  pressures  measured  by  a  scale  corresponding  to  the 
indicator  spring  are  as  follows : 

18,  26,  28.4,  27.8,  27,  24.2,  19,  16,  14.3,  7.2.     Find  the  m.e.p. 

Solution:  We  add  the  pressures  and  find  the  sum  207.9. 
Divide  this  by  10  and  we  have  20.79  or  2o-8  Ib.  as  the  value  of 
the  m.e.p. 

(6)  From  the  two  cards  of  a  pair  the  values  of  the  m.e.p.  are 
found  to  be  28.6  for  one  end  and  32.2  for  the  other.    The  piston 
area  is  1,213  scl-  m->  the  stroke  39  in.  and  the  revolutions  102. 
Find  the  I.H.P.  neglecting  the  effect  due  to  the  area  of  piston 
rod. 

Solution:  The  m.e.p.  for  the  whole  revolution  is  the  mean 
of  the  values  for  the  two  ends  or  m.c.p.  —  (28.6  X  32.2)  -f-  2 

=  304- 

Then  stroke  in  feet  =  39  -^  12  =  3.25. 

Then  I.H.'p.  :  =  2  X  3°'4  X  3'25  x   I213  X   I02 

33000 


*  This  abbreviation  is  often  used  for  the  term  mean  effective  pressure. 


424  PRACTICAL  MARINE  ENGINEERING. 

Multiplying  out  the  factors  of  the  numerator  and  dividing  by 
the  denominator  we  find  I.H.P.  =  741  Ans. 
(7)  Given  the  following : 

Diam.  of  cylinder  =  24  in. 
.  Diam.  of  piston  rod  =  5  in. 
m.e.p.  from  head  end  or  pi  =  63.4  Ib. 
m.e.p.  from  crank  end  or  p*  =  58.8  Ib. 
Stroke  =  36  in. 
Revolutions  no. 

Find  the  I.H.P.  both  with  and  without  the  allowance  for  the 
area  of  piston  rod. 
Solution: 

Area  of  24  inch  piston  or  Ai  =  452.4  sq.  in. 
Area  of  5  inch  piston  rod  or  a  =  19.6  sq.  in. 
Effective  area  of  lower  side  of  piston  =  difference,  or  A* 
=  432.8  sq.  in. 

Then  neglecting  the  effect  of  the  rod  we  should  say : 
m.e.p.  =  (63.4  +  58.8)  -r-  2  =  61.1 

2   X   61.1   X   3  X  452-4  X    no 
33000 

Working  this  out  we  find:  I.H.P.  =  552.8. 
Taking  account  of  the  piston  rod  area  we  have  for  the  head 
end: 

H    =  63-4  X   3  X  452.4  X   no   =2g6  g 

33000 

For  the  crank  end : 

=  58.8x3^433-8X110   = 
33000 

Adding  we  have : 
H  =  541.3. 

There  is  thus  seen  to  be  in  this  case  a  difference  of  11.5 
horse  power,  constituting  an  error  by  the  first  method  of  some 
considerable  amount.  It  is  readily  seen  that  this  error  will  be 
relatively  less  the  larger  the  cylinder,  especially  in  the  cylinders 
of  a  multiple  expansion  engine.  Thus  in  the  case  given  which 
was  for  the  H.P.  cylinder  of  a  triple  expansion  engine  the  error 
is  11.5  horse  power,  or  about  2  per  cent.  For  the  I. P.  cylinder 
the  error  would  be  not  far  from  4.5  horse  power  or  about  .8  per 
cent.,  while  for  the  L.P.  cylinder  it  would  be  perhaps  two  horse 
power  or  about  .3  per  cent.  This  would  give  a  resultant  error 


and  J.H.P  =  /'X6..ix3X45'.4Xiiox 
V  33000  / 


INDICATORS   AND   INDICATOR    CARDS. 


425 


of  about  i  per  cent,  for  the  engine  as  a  whole.  While  these 
figures  would  vary  with  particular  circumstances,  they  will  serve 
to  illustrate  the  nature  of  the  error,  and  the  methods  given  show 
how  to  avoid  it  when  so  desired. 

[4]  Combined  Indicator  Cards. 

The  cards  taken  from  the  various  cylinders  of  a  multiple 
expansion  engine,  as  for  example  those  of  Fig.  265,  may  be 


HIGH  PRESSURE 


ATMOSPHERIC  LINE 


ATMOSPHERIC  LINE 


Fig.  265.     Set  of  Indicator  Cards  from  Triple  Expansion  Engine. 

combined  in  such  a  manner  as  to  show  very  instructively  the 
continuous  history  of  the  expansion  of  the  steam,  that  is  the 
continuous  relation  between  volume  and  pressure  as  the  steam 


4*6  PRACTICAL  MARINE  ENGINEERING. 

passes  through  the  engine.  To  effect  this  combination  it  is 
necessary  to  lay  down  the  various  cards  in  one  diagram  and  all 
to  the  same  scale  of  volume  and  pressure.  The  details  of  the 
operation  may  be  sketched  out  in  the  following  steps : 

(1)  In  Fig.  266  take  the  two  lines  at  right  angles,  OX  and 
OY,  the  former  as  an  axis  of  volume  and  the  latter  as  an  axis  of 
pressure. 

(2)  Determine  in  cubic  feet  for  each  of  the  cylinders  the 
volume  of  the/  clearance  (Sec.  67),  and  the  volume  swept  by  the 
piston. 

(3)  Lay  off  the  lines  AB,  CD,  EF  at  such  distances  from 
OY  as  to  represent  respectively  the  clearance  volume  in  the 


Marine  Engineering  Q    X. 

Fig.  266.     Combined    Cards    from   Triple    Expansion    Engine. 

H.P.,  I. P.,  and  L.P.  cylinders,  taking  care  to  select  the  scale  of 
volume  such  that  the  L.P.  volume  plus  its  clearance  as  measured 
between  the  lines  OY  and  GK  will  come  within  the  desired  limits 
of  the  diagram. 

(4)  Lay  off  on  each  card  the  line  of  zero  pressure  or  the 
perfect  vacuum  line,  as  shown  by  OX  in  the  small  diagram  A. 

(5)  Take  next  the  H.P.  card  as  at  A  for  example,  and  select 
any  point  such  as  P.     Measure  in  any  convenient  units  the  dis- 
tances MP  and  MN  :  multiply  the  volume  of  the  cylinder  by  the 
former  and   divide  by  the  latter.     This  will   give  the  volume 


INDICATORS  AND  INDICATOR  CARDS.  427 

swept  in  the  H.P.  cylinder  from  the  beginning  of  the  stroke  to 
the  point  P. 

(6)  The  corresponding  point  P  of  the  combined  diagram 
is  then  found  by  measuring  from  AB  a  distance  HP  representing 
this  volume,  and  from  OX  a  distance  JP  representing  the  pres- 
sure PO  on  the  card.     This  will  give  the  point   P,  and  other 
points  are  found  in  a  similar  manner,  as  many  as  may  be  needed 
to  determine  the  form  of  the  card  as  shown.    It  is  to  be  especially 
noted  that  the  H.P.  card  of  the  combined  set  is  the  same  as  that 
at   \  but  drawn  simply  with  different  scales,  and  therefore  more 
or  less  distorted  in  appearance. 

(7)  The  points  necessary  to  determine  the  other  cards  of 
the  combination  a«e  found  in  a  precisely  similar  manner,  re- 
membering that  in  each  case  volume  is  measured  from  the  clear- 
ance line  CD  or  EF,  while  the  pressure  must  be  measured  from 
the  line  of  zero  pressure  for  the  card  and  laid  off  from  the  cor- 
responding line  OX  of  the  combined  set. 

This  diagram  shows  the  general  manner  in  which  the  steam 
expands  on  its  way  through  the  engine.  An  expansion  line 
PQ  shows  the  general  law  of  expansion  as  a  continuous 
operation. 

PR  is  an  ideal  expansion  line  laid  down  as  a  hyperbola,  all 
points  in  the  curve  corresponding  to  the  condition  that  the 
product  of  volume  by  pressure  shall  be  constant,  or  in  symbols, 
pv  —  Constant.  This  shows  the  result  of  the  so-called  true 
hyperbolic  expansion  law,  and  as  appears  from  the  diagram,  the 
actual  expansion  line  is  somewhat  below  this  ideal  line. 

The  equation  to  the  actual  expansion  line  may  be  expressed 
in  the  form  pv"  =  Constant,  where  n  is  an  exponent  having 
values  usually  lying  between  1.15  and  1.2.  The  equation  pv1-18 
may  be  taken  as  very  commonly  representing  this  line  in  good 
average  practice.  The  extent  to  which  the  area  bounded  by 
the  line  PR  and  the  clearance  lines  on  the  left  is  well  filled  in.  is 
an  indication  of  the  degree  to  which  the  performance  of  the 
actual  engine  approaches  that  of  an  engine  having  true  hyper- 
bolic expansion  and  with  indicator  cards  as  shown  in  Fig.  252. 
The  relation  between  the  actual  engine  and  such  an  ideal  case 
is  usually  expressed  by  a  percentage  factor  known  as  the  "card 
factor."  For  good  practice  with  triple  expansion  engines,  this 
factor  will  be  found  from  .60  to  .70.  With  quadruple  expansion 
engines  representative  values  are  found  from  .55  to  .60. 


428  PRACTICAL  MARINE  ENGINEERING. 

The  diagrams  of  figures  265  are  reproduced  from  an  actual 
case  and  may  be  considered  as  representing  good  modern 
practice  in  general  character  and  form. 

At  this  point  reference  may  be  made  to  the  effect  on  the 
distribution  of  power  in  a  compound  or  multiple  expansion 
engine,  of  linking  up  or  cutting  off  earlier  in  the  intermediate 
or  low  pressure  cylinders.  Taking  first  the  case  of  a  compound, 
linking  up  or  shortening  the  cut-off  on  the  L.  P.  cylinder  will 
increase  the  power  in  this  cylinder  and  decrease  it  in  the  high. 
This  result  at  first  sight  seems  contradictory  to  common  ex- 
perience, because  in  a  single  cylinder  we  are  accustomed  to 
associate  an  earlier  cut-off  with  decrease  of  power.  In  the  case 
of  the  compound,  however,  cutting  off  earlier  in  the  L.P.  cylin- 
der gives  a  higher  back  pressure  in  the  H.P.  cylinder  and  a 
consequently  higher  initial  pressure  in  the  L.P.  cylinder,  and 
thus  results  in  an  actual  addition  to  the  L.P.  indicator  card  area 
instead  of  a  decrease  as  in  the  case  of  a  single  cylinder.  At  the 
same  time  the  area  of  the  H.P.  card  will  be  reduced  and  the 
power  developed  in  this  cylinder  will  be  decreased  correspond- 
ingly. Similarly  for  a  multiple  expansion  engine  and  in  general, 
cutting  off  earlier  in  any  of  the  cylinders  beyond  the  first  or 
H.P.  will  result  in  an  increased  back  pressure  for  the  next  pre- 
ceding cylinder,  and  in  a  higher  initial  pressure  for  the  cylinder 
itself,  and  thus  in  an  actual  addition  to  the  area  of  the  indicator 
card  and  a  corresponding  subtraction  from  the  area  of  the  card 
for  the  cylinder  preceding. 

Thus  in  Fig.  266,  cutting  off  earlier  in  the  L.P.  cylinder 
will  result  in  raising  the  upper  line  of  the  L.P.  and  lower  line 
of  the  I. P.  cards,  and  thus  in  increasing  the  area  of  the  former 
and  decreasing  that  of  the  latter.  In  like  manner  cutting  off 
earlier  in  the  intermediate  cylinder  will  result  in  raising  the 
upper  line  of  the  I. P.  and  lower  line  of  the  H.P.  cards  and  thus 
in  increasing  the  area  of  the  former  and  decreasing  that  of 
the  latter.  In  like  manner  cutting  off  later  in  any  cylinder  be- 
yond the  H.P.  will  result  in  similar  changes  but  in  the  opposite 
direction.  Thus  a  later  cut-off  in  the  I. P.  cylinder  will  decrease 
the  power  developed  in  that  cylinder,  and  increase  the  power 
developed  in  the  H.P.  cylinder.  It  thus  results  that  a  combi- 
nation of  changes  such  as  a  later  cut-off  in  the  I.  P.  cylinder  and 
earlier  cut-off  in  the  L.P.  will  both  tend  to  decrease  the  power 
developed  in  the  I. P. ;  while  an  earlier  cut-off  in  the  L.P.  cylinder 


INDICATORS  AND  INDICATOR  CARDS.  4*9 

and  a  later  cut-off  in  the  H.P.  will  both  tend  toward  an  increase 
of  power  developed  in  the  I. P. 

Sec.  56.   STEAM  ENGINE  INDICATORS. 

[i]  Descriptive. 

The  indicator  card  has  already  been  described  in  Sec.  55. 
It  is  the  purpose  of  the  indicator  to  draw  this  card.  It  must 
therefore  provide  for  the  proper  combination  of  these  move- 
ments, (i)  A  movement  in  step  with  the  piston  and  propor- 
tional to  it  in  amount  so  that  all  horizontal  distances  on  the  card 
shall  bear  a  constant  proportion  to  the  corresponding  parts  of 
the  stroke.  (2)  A  movement  at  right  angles  to  that  in  (i)  and 
in  direct  proportion  to  the  pressure  per  square  inch  on  the  pis- 
ton in  the  end  of  the  cylinder  to  which  the  indicator  is  con- 
nected. 

The  combination  of  these  movements  will  then  result  in  a 
diagram  such  as  those  shown  in  Sec.  55,  and  giving  at  each 
point  of  the  stroke  the  pressure  on  the  piston  as  desired,  the 
upper  line  showing  the  pressure  which  urges  the  piston  for- 
ward on  one  stroke  and  the  lower  line  the  pressure  which  re- 
sists its  movement  backward  on,  the  return  stroke. 

In  Fig.  267  a  modern  indicator  is  shown.  A  is  a  drum  to 
which  the  paper  is  attached  by  means  of  the  clips  as  shown. 
This  drum  is  given  a  motion  back  and  forth  about  its  axis  by 
means  of  a  connection  with  the  crosshead  through  the  so-called 
"reducing  motion."  By  this  means  the  drum  is  given  a  motion 
of  some  three  to  five  inches  in  extent,  just  in  step  with  the 
motion  of  the  piston  and  proportional  to  it  in  amount.  B  is 
the  indicator  cylinder  or  barrel  connecting  with  the  end  of  the 
engine  cylinder  from  which  the  card  is  to  be  taken.  Within 
the  cylinder,  as  shown,  is  a  piston  with  a  coiled  steel  spring 
above,  resisting  pressure  from  below  the  piston  upward.  To 
the  piston  rod  is  attached  a  linkage  carrying  at  the  end  of 
the  arm  P  the  pencil  point  which  is  to  trace  the  diagram  upon 
the  paper  carried  by  the  drum.  The  connection  between  the 
linkage  and  the  piston  rod  is  such  that  the  former  may  be  swung 
freely  about  the  cylinder  upon  a  ring  to  which  it  is  attached. 
The  pencil  may  thus  be  brought  into  contact  with  the  paper  on 
the  drum  or  withdrawn  from  it  as  desired.  An  adjustable  screw 
stop  is  provided,  and  so  arranged  as  to  arrest  the  movement 


43° 


PRACTICAL  MARINE  ENGINEERING. 


of  the  pencil  motion  when  swung  around  by  the  hand,  and  thus 
allow  only  light  contact  between  the  pencil  point  and  the  paper. 
In  some  cases  a  brass  point  is  used  instead  of  a  pencil,  the 
cards  being  of  paper  specially  prepared  so  that  the  brass  will 
leave  a  black  mark  upon  it.  Such  points  are  strong  and  require 
no  sharpening  except  at  long  intervals. 

The  object  of  the  linkage  which,  forms  the  pencil  motion 
is  to  magnify  the  movement  of  the  indicator  piston,  and  thus 


Marine  Engineering 


Fig.  267.     Steam    Engine   Indicator. 


to  allow  the  use  of  stiff  springs  with  a  corresponding  small 
movement  of  spring  and  piston.  With  high  revolutions  es- 
pecially, this  is  found  necessary  in  order  to  reduce  as  far  as 
possible  the  disturbance  in  the  diagram  due  to  the  inertia  of 
the  moving  parts  of  the  indicator.  The  linkage  is  thus  a  form 
of  multiplying  motion,  or  a  reducing  motion  reversed,  and  it 


INDICATORS  AND  INDICATOR  CARDS.  431 

should  give  to  the  pencil  a  movement  exactly  proportional  to 
that  of  the  piston,  but  3  to  5  times  greater  as  may  be  desired. 

The  relation  between  the  pressure  per  square  inch  and  the 
actual  movement  at  the  pencil  point  fixes  the  so-called  scale  of 
the  spring.  This  depends  also  on  the  actual  area  of  the  indi- 
cator piston,  which  is,  however,  usually  about  one-half  square 
inch.  Thus  a  40  pound  spring  means  a  spring  such  that  a  pres- 
sure of  40  pounds  per  square  inch  on  the  indicator  piston,  or  say 
an  actual  load  of  20  pounds,  will  produce  a  movement  of  one 
inch  at  the  pencil  point. 

By  means  then  of  the  piston,  spring  and  linkage,  the  second 
of  the  necessary  movements  as  mentioned  above  is  thus  pro- 
duced. 

Returning  to  the  drum  the  first  of  the  motions  above  noted 
is  obtained  by  some  form  of  reducing  motion  as  described  be- 
low. The  connection  between  the  drum  and  the  reducing  mo- 
tion is  usually  made  by  means  of  a  cord  C  wrapped  around 
a  groove  in  the  base  as  shown.  The  cord  thus  serves  to  pull 
the  drum  around  in  one  direction  while  the  return  stroke  is 
made  by  means  of  a  coiled  spring  in  tfie  base.  This  spring  op- 
poses the  motion  given  by  the  cord,  and  is  therefore  coiled  up 
during  the  forward  stroke.  As  soon,  however,  as  the  pull  of  the 
cord  ceases  the  spring  takes  charge  and  uncoiling  carries  the 
drum  in  the  reverse  direction  as  fast  as  the  cord  will  allow,  thus 
keeping  the  latter  taut  and  insuring  the  motion  of  the  drum  in 
step  with  the  main  piston  in  both  directions  as  accurately  as  the 
form  of  reducing  motion  may  determine. 

A  separate  indicator  may  be  provided  for  each  end  of  the 
cylinder,  or  by  suitable  pipe  connections  and  a  three  way  cock, 
one  indicator  may  be  made  to  serve  for  both  ends.  In  any 
case  the  cock  which  shuts  off  the  indicator  must  be  so  arranged 
that  when  shut  off  from  the  cylinder  the  space  below  the  piston 
will  be  connected  to  the  outside  air.  The  piston  with  equal  air 
pressure  on  both  sides  will  then  come  to  a  position  of  equilib- 
rium, and  the  atmospheric  line  may  be  drawn. 

[2]  Reducing  Motions. 

The  purpose  of  the  reducing  motion  has  already  been 
stated.  There  are  many  different  ways  in  which  the  desired 
movement  may  be  given  to  the  drum,  some  of  them  accurate 
in  geometrical  principle  and  some  only  approximate. 


432 


PRACTICAL  MARINE  ENGINEERIXG. 


One  of  the  most  common  is  by  means  of  links,  levers  and 
bell-cranks.  The  simplest  of  such  forms  is  shown  in  Fig.  268. 
A  is  a  pin  attached  to  the  crosshead.  AB  is  a  short  link  con- 
necting the  crosshead  to  a  lever  BD  pivoted  at  C.  The  point 
D  will  then  move  in  step  and  nearly  in  constant  proportion  to 
the  piston,  and  from  D  the  motion  for  the  drum  may  be  taken, 
either  by  a  cord  direct,  or  from  the  end  E  of  a  rod  DE  moving 
as  shown.  In  such  cases  the  cord  should  run  in  continuation 
of  the  line  DE  and  not  off  at  an  angle  as  EF  or  DH.  As  a 
general  rule  in  all  such  cases,  the  reducing  motion  should  be 
so  adjusted  that  the  cord  part  should  not  undergo  changes  of 
angular  direction,  or  at  least  such  changes  should  be  made  as 
small  as  possible.  Thus  in  Fig.  269  suppose  the  point  from 


Fig.  268.     Reducing  Motion. 


V 


B"  Marine  £n 


gineering 


Fig.  269.     Reducing  Motion. 

which  the. motion  is  taken  to  move  through  a  path  AB,  and 
the  indicator  guide  pulley  to  be  at  P.  Then  at  one  extreme  the 
cord  will  be  represented  by  PA,  and  at  the  other  by  PB.  Such  a 
change  in  the  angular  direction  of  the  cord  relative  to  the  line 
of  motion  AB  will  result  in  error,  and  should  be  avoided  by 
bringing  P  over  AB  or  AB  under  P.  It  is  not  necessary  that 
the  motion  of  the  point  E  Fig.  268  should  be  vertical  so  long 
as  the  gear  is  so  arranged  as  to  reduce  to  a  minimum  all  angu- 
lar changes  in  cords  and  connecting  links.  Thus  the  arrange- 
ment of  Fig.  270,  while  containing  a  large  number  of  joints  and 
parts,  may  be  as  nearly  correct  as  the  simpler  form  of  Fig.  268. 
Instead  of  taking  the  motion  direct  from  D  a  link  DG  con- 
nects this  point  with  a  bell-crank  GHI  pivoted  at  H.  Then  a 


INDICATORS   AND   INDICATOR    CARDS. 


4:3 


second  link  1J  connects  this  to  a  second  bell-crank  JKL  and  a 
rod  LE  guided  at  M  gives  a  point  E  from  which  the  motion- 
may  be  taken,  or  if  more  convenient  the  rod  LE  may  be  dis- 
pensed with  and  the  motion  taken  from  L  direct.  Such  a  com- 
plication of  gear  is  of  course  not  desirable,  and  the  arrangement 
is  shown  simply  as  an  illustration  of  a  combination  of  links  and 
bell-cranks  which  would  still  give  the  motion  required. 


A  - 

4- 


Fig.  270.     Reducing   Motion. 

All  such  forms  of  reducing  motion  are  approximate  and  not 
geometrically  exact.  The  error  is,  however,  in  most  cases  small 
and  is  usually  neglected,  though  if  desired  its  nature  and  extent 
may  be  investigated  by  a  suitable  geometrical  analysis  of  the 
gear. 

Instead  of  taking  the  motion  from  the  crosshead  by  means 
of  a  short  link  as  AB  Fig.  268,  a  lever  BD  Fig.  271  is  some- 
times provided,  having  a  forked  end  and  pivoted  at  C  or  D.  A 
pin  on  the  crosshead  working  in  the  slot  or  forked  end  gives  the 
to  and  fro  motion  to  the  lever,  while  from  D  or  C  the  desired 
motion  is  taken. 


Fig.  271.     Reducing   Motion. 

Instead  of  attaching  the  cord  direct  to  C  for  example,  a 
sector  of  wood  PQD  with  center  at  D  is  attached  to  the  arm, 
and  the  string  is  led  off  from  the  face  of  the  sector.  Such  a 
sector  may  also  be  employed  with  the  arrangements  shown  in 
Figs.  268  and  270.  None  of  these  motions  is  geometrically 
exact. 

A  form  of  pantograph  consisting  of  jointed  rods  as  shown 
in  Fig.  272,  may  sometimes  be  used  when  there  is  room  for  it 


434 


PRACTICAL  MARINE  ENGINEERING. 


to  work  freely.  A  is  attached  to  the  crosshead  and  D  or  E  is 
the  fixed  pivot.  Then  the  other  point  E  or  D  will  provide  a 
motion  for  the  indicator  drttm  which  is  geometrically  exact. 
Here  again  however,  the  string  should  be  so  led  that  its  angu- 
larity will  not  vary. 

Instead  of  this  arrangement  of  links  the  so-called  lazy-tongs 
as  shown  in  Fig.  273  is  sometimes  employed.  This  is  also 
geometrically  exact,  and  is  in  fact  an  equivalent  to  the  panto- 
graph in  Fig.  272,  without  requiring  quite  as  much  room. 

Various  combinations  of  pulleys  may  also  be  used,  as  illus- 
trated in  Fig.  274.  AB  is  an  arm  projecting  from  the  crosshead 
and  moving  with  it.  To  the  end  B  of  this  arm  is  attached  a 
cord  wrapping  around  a  light  pulley  P.  Q  is  a  smaller  pulley  on 


Marine  UnjiMerinj 

Fig.  272.     Pantograph    Reducing   Motion. 


Fig.  273.     Lazy  Tongs  Reducing  Motion. 

the  same  axis  and  moving  with  P.  Wrapped  on  this  is  a  cord 
CD,  which  may  be  led  off  in  various  directions  to  the  indicator  as 
shown  by  CD,  CD^  CDL>.  This  gear  is  geometrically  exact. 

Various  other  forms  of  reducing  motion  are  also  to  be  met 
with,  but  those  described  will  be  suffcient  to  show  the  forms 
most  commonly  available  for  marine  practice. 

[3]  Taking  an  Indicator  Card. 

The  instrument  should  first  be  examined  and  put  into  proper 
condition  and  adjustment.  This  should  include  the  following 
points : 

(i)  The  joints  should  all  work  freely,  but  without  lost 
motion. 


INDICATORS   AND   INDICATOR   CARDS. 


435 


(2)  The  piston  should  not  bind  nor  should  it  be  so  loosely 
fitted  as  to  allow  serious  leakage.    A  slight  leakage  is,  however, 
better  than  too  snug  a  fit. 

(3)  The  working  surfaces  of  the  barrel  and  piston  should 
be  carefully  wiped  and  oiled.  This  should  be  repeated  from  time 
to  time  when  a  series  of  cards  is  being  taken.    The  joints  of  the 


Fig.  274.     Reducing  Motion. 

pencil  motion  should  also  be  lubricated  with  clock  oil  as  often  as 

may  be  required. 

(4)  The  pencil  points  should  be  sharpened  and  the  screw 

stop  so  adjusted  that  the  point  can  rest  only  lightly  on  the  paper. 
The  operation  of  taking  the  card  itself  is  briefly  as  follows : 
The  indicator  is  attached  to  the  cock,  a  blank  card  is  placed 

on  the  drum  and  the  cord  connection  is  adjusted  so  that  the 

drum  will  have  the  proper  stroke  without  coming  against  the 


Fig.  275.     Putting  on  an  Indicator  Card. 


stop  at  either  end.  In  attaching  the  blank  card  the  most  con- 
venient way  will  be  to  bend  the  sheet  of  paper  around  and  grasp 
both  edges  between  the  thumb  and  forefinger  as  at  AB  in  Fig. 
275a.  Then  slip  over  the  drum  and  under  the  clips  so  that  the 
latter  will  come  outside  the  paper  as  shown  at  PQ,  b.  Then 
slip  the  paper  down  into  place,  pull  and  adjust  so  that  it  fits  snug- 


436  PRACTICAL  MARINE  ENGINEERING. 

ly,  and  bend  the  edges  back  as  in  c.  The  cord  is  then  hooked 
on  to  the  reducing  motion  and  the  drum  takes  up  its  movement 
with  the  main  piston.  The  cock  is  then  opened  to  the  end  of 
the  cylinder  from  which  the  diagram  is  desired,  and  the  pencil 
immediately  takes  up  its  motion  corresponding  to  the  varying 
pressures  of  the  steam.  The  indicator  piston  should  be  allowed 
to  work  in  this  way  for  a  few  strokes,  or  until  everything  is 
warmed  up  into  working  condition. 

When  everything  is  in  readiness  the  pencil  motion  is  moved 
up  against  the  stop  so  that  the  pencil  resting  lightly  on  the  paper 
will  trace  its  path  for  a  complete  revolution  or  longer  if  de- 
sired. Then  remove  and  shut  off  the  indicator  from  the  cylinder. 
This  will  connect  it  with  the  air,  the  indicator  piston  will  come 
to  equilibrium  under  atmospheric  pressure,  and  the  atmospheric 
line  may  then  be  drawn.  The  drum  connection  is  then  un- 
hooked, the  paper  removed,  a  fresh  one  replaced,  and  the  next 
card  taken  when  desired.  If  one  indicator  is  used  for  both  ends 
of  the  cylinder,  both  cards  should  be  taken  on  the  same  paper 
with  as  small  an  interval  between  as  possible.  The  cock  is 
swung  over  for  one  end  and  the  card  taken,  and  then  imme- 
diately swung  over  for  the  other  end  and  the  second  card  taken 
without  loss  of  time.  The  cock  is  then  closed  off  connecting 
the  indicator  with  the  air,  and  the  atmospheric  line  is  then 
drawn. 

Each  card  as  it  is  removed  from  the  indicator  should  be 
marked  with  sufficient  data  to  identify  it,  and  make  possible  its 
use  for  the  purpose  intended.  This  should  include  at  least  the 
following  items : 

(1)  Cylinder. 

(2)  End  from  which  card  is  taken. 

(3)  Revolutions. 

(4)  Scale  of  spring. 

(5)  If  a  series  of  cards  is  being  taken  the  time  and  serial 
number  should  also  be  set  down. 

The  various  other  items  usually  printed  on  the  back  of  the 
card  may  be  filled  in  at  a  later  time  as  may  be  convenient.  When 
cards  from  both  ends  are  taken  on  one  paper,  we  must  be  able 
to  assign  each  to  its  proper  end  of  the  cylinder.  The  most  cer- 
tain way  of  determining  this  is  to  shut  off  the  connection  to  one 


INDICATORS   AND   INDICATOR   CARDS.  437 

end  of  the  cylinder  entirely,  and  then  take  the  card  from  the 
other  end.  It  will  thus  appear  how  the  card  from  this  end  lies 
on  the  paper,  whether  with  admission  line  to  the  right  or  left, 
and  this  will  show  how  to  mark  the  entire  series  of  cards  taken 
with  the  same  arrangement  of  reducing  gear,  etc. 


438  PRACTICAL  MARINE  ENGINEERING. 


CHAPTER  IX. 

SPECIAL  TOPICS  AND  PROBLEMS. 

Sec.  57.  HEAT  AND  THE  FORMATION  OP  STEAM. 

[i]  Constitution  of  Matter. 

For  the  purpose  of  explaining  or  discussing  the  relations  be- 
tween matter  and  the  forces  of  nature,  all  substances  are  sup- 
posed to  be  composed  of  enormously  large  numbers  of  in- 
definitely small  parts  called  molecules,  each  one  of  which  is 
supposed  to  be,  in  fact,  the  smallest  portion  of  the  substance 
which  can  exhibit  its  various  properties.  These  molecules  are 
furthermore  not  at  rest,  but  are  supposed  to  be  in  a  state  of 
more  or  less  violent  agitation  or  motion.  If  the  motion  of  each 
molecule  is  about  a  fixed  center  so  that  they  all  retain  their 
average  positions  fixed  in  the  body,  it  is  said  to  be  a  solid  or  in 
the  solid  state.  If  the  motion  of  the  molecules  is  about  centers 
which  themselves  are  free  to  move  about  in  any  direction,  so 
that  the  average  position  of  the  molecules  is  not  fixed  and  the 
body  readily  changes  its  form,  it  is  said  to  be  a  liquid  or  in  the 
liquid  state.  If  the  motion  of  the  molecules  is  in  straight  lines 
hither  and  thither,  bound  to  no  center  or  location,  but  ever 
striving  to  fly  as  far  apart  as  possible,  the  substance  is  said  to 
be  a  gas  or  in  the  gaseous  state. 

In  the  solid  and  liquid  states  the  molecules  are  bound  to- 
gether by  forces  of  molecular  attraction,  so  that  they  tend  to 
maintain  about  the  same  average  distance  apart,  and  thus  to  fill 
the  same  volume.  Any  attempt  to  change  this  average  distance 
between  the  molecules  and  thus  to  make  the  volume  larger  or 
smaller,  must  deal  with  these  molecular  forces.  The  only  prac- 
ticable way  of  doing  this  is  through  the  agency  of  heat,  as  we 
shall  see  in  the  next  section.  In  a  gas  the  forces  binding  the 
molecules  together  have  been  overcome,  and  the  molecules  have 


SPECIAL    TOPICS   AND   PROBLEMS.  439 

been  separated  so  much  further  apart  that  all  traces  of  these 
attractive  forces  have  disappeared,  and  instead  we  now  have  a 
repulsive  force  acting  between  the  molecules  and  urging  them 
as  far  apart  as  the  limits  of  the  volume  which  contains  them 
will  allow.  Due  to  this  property  a  gas  will  expand  and  fill  any 
volume,  no  matter  how  large,  the  repulsive  force  or  force  of  ex- 
pansion, however,  becoming  weaker  as  the  volume  increases 
and  the  average  distance  between  the  molecules  becomes  greater 
and  greater. 

[2]  Heat. 

(i)  Heat  and  Its  Relation  to  Matter. — We  know  energy  as  the 
capacity  for  doing  work.  Also  the  energy  of  motion  is  called 
kinetic  energy,  while  the  energy  of  position  or  location  relative 
to  a  given  force,  is  called  potential  energy. 

Heat  is  one  of  the  many  forms  of  energy.  It  is,  in  fact,  the 
energy  of  the  molecule,  and  the  heat  in  a  body  means  therefore 
simply  the  amount  of  such  molecular  energy  which  the  body 
possesses.  This  energy  of  the  molecule  is  partly  kinetic  or  due 
to  its  motion,  and  partly  potential  due  to  its  position  relative  to 
the  molecular  forces  which  act  upon  it.  The  addition  of  heat 
to  a  body  or  its  subtraction  from  a  body  means  therefore  the 
addition  or  subtraction  from  the  energy  of  its  molecule,  and 
hence  the  addition  to  or  subtraction  from  its  store  of  molecular 
energy.  This  addition  or  subtraction  of  heat  is  always  accom- 
panied by  a  series  of  changes  in  the  state  or  condition  of  the 
body. 

Thus  if  heat  be  added  to  a  lump  of  ice  at  the  melting  point 
or  32°  Fah.  it  first  melts  or  changes  from  a  solid  to  a  liquid, 
remaining  at  the  constant  temperature  of  32°  and  slightly  con- 
tracting in  volume  meanwhile.  If  heat  is  still  farther  added  the 
water  grows  warmer  to  the  touch  and  as  shown  by  the  ther- 
mometer. At  the  same  time  it  continues  to  contract  slightly  till 
it  reaches  a  temperature  of  about  39°  Fah.  and  then  slowly  ex- 
pands. If  under  atmospheric  pressure  the  increase  of  tempera- 
ture and  volume  will  continue  with  the  addition  of  heat  until 
the  thermometer  marks  a  temperature  of  212°  Fah.  Then  the 
further  addition  of  heat  occasions  no  further  elevation  of  tem- 
perature, but  instead,  a  new  change  of  state.  The  water  now 
passes  into  the  state  of  vapor  or  steam,  the  temperature  of  both 
the  water  and  the  vapor  formed  from  it  remaining  meanwhile 


440  PRACTICAL  MARINE  ENGINEERING. 

constantly  at  the  fixed  temperature  of  212°.  After  the  water  is 
completely  vaporized,  if  the  vapor  be  inclosed  in  a  chamber  of 
fixed  volume  and  heat  still  further  added,  it  will  then  be  found 
that  the  pressure  and  temperature  will  continue  to  increase  so 
long  as  additional  heat  is  supplied.  If  instead  the  pressure  is 
kept  constant,  the  volume  and  temperature  will  increase  as  heat 
is  added.  If  the  temperature  is  kept  constant,  the  pressure  will 
fall  as  the  volume  is  increased. 

From  the  start  then,  as  more  and  more  heat  has  been  added, 
the  water  has  exhibited  successively  the  three  states  of  matter. 
As  ice  it  is  a  solid;  in  its  usual  state  or  between  32°  and  212° 
under  atmospheric  pressure,  it  is  a  liquid;  and  after  it  is  com- 
pletely vaporized  and  heat  is  still  further  added  so  as  to  carry 
the  conditions  considerably  beyond  those  at  which  the  vapor 
was  formed,  it  becomes  a  gas. 

We  must  here  explain  the  difference  which  may  be  implied 
in  the  words  gas  and  vapor.  When  a  substance  first  changes 
from  the  liquid  to  the  gaseous  state,  or  while  the  pressure, 
volume  and  temperature  are  near  those  corresponding  to  such 
a  change,  the  substance  is  more  strictly  called  a  vapor,  or  is  said 
to  be  in  the  vaporous  condition.  If  the  substance  is  in  the  gaseous 
state  but  with  pressure,  volume  and  temperature  conditions  far 
removed  from  those  corresponding  to  the  change  of  state,  the 
substance  is  more  generally  called  a  gas.  There  is  no  sharp  line 
of  difference  between  a  vapor  and  a  gas.  The  former  means 
simply  a  substance  in  the  gaseous  state,  but  at  or  near  the  con- 
ditions corresponding  to  the  process  of  change  from  one  state 
to  the  other,  while  the  latter  means  likewise  a  substance  in  the 
gaseous  state,  not  far  removed  from  the  conditions  correspond- 
ing to  the  process  of  change  of  state. 

There  are  thus  two  chief  kinds  of  change  which  the  applica- 
tion of  heat  may  produce. 

(a)  It  may  change  the  temperature  of  a  substance  accom- 
panied by  a  change  of  pressure  or  volume  or  both,  but  without 
change  of  state. 

(b)  It  may  produce  a  change  of  state  as  from  solid  to  liquid 
or  liquid  to  vapor,  accompanied  usually  by  a  change  of  volume, 
but  without  change  of  temperature.     If,  however,  the  pressure 
varies  during  the  change  of  state,  then  the  temperature  at  which 
the  change  occurs  will  also  vary,  but  there  will  be  no  change 
of  temperature  directly  accompanying  the  change  of  state.    In 


SPECIAL    TOPICS   AND   PROBLEMS.  441 

consequence,  during  the  change  from  solid  to  liquid  or  vice  versa, 
the  temperatures  of  both  are  the  same,  and  similarly  during  the 
change  from  liquid  to  vapor  or  vice  versa,  the  temperatures  of 
both  are  the  same. 

It  must  be  understood  when  changes  are  referred  to  as 
depending  on  the  addition  of  heat,  that  the  subtraction  of  heat 
will  produce  changes  in  exactly  the  opposite  direction.  Thus 
if  the  addition  of  heat  causes  a  body  to  expand,  the  subtraction 
will  cause  it  to  contract :  if  the  addition  causes  an  increase  of 
pressure  the  subtraction  will  cause  a  decrease :  if  the  addition 
causes  a  change  of  the  state  from  liquid  to  vapor,  the  subtrac- 
tion will  cause  a  change  from  vapor  to  liquid,  etc. 

(2)  Sensible  and  Latent  Heat. — Heat  which  causes  a  change 
of  temperature  in  a  body,  as  when  water  is  heated  and  becomes 
hotter  to  the  touch  or  to  the  thermometer,  is  called  sensible  heat. 
This  corresponds  to  a  change  in  the  kinetic  energy  of  the 
molecule,  so  that  increase  of  velocity  of  the  molecule  and  in- 
crease of  its  kinetic  energy  correspond  within  the  substance  to 
the  growing  hotter  to  the  touch  and  to  increase  of  temperature 
as  observed  on  the  outside. 

Heat  which  is  involved  in  a  change  of  state  but  which  pro- 
duces no  effect  on  the  temperature  of  the  substance  (as  in  the 
melting  of  ice  at  32°  or  the  boiling  of  water  at  212°)  is  called 
latent  heat.  This  corresponds  to  a  change  in  the  potential  energy 
of  the  molecule  so  that  an  increase  in  the  average  distance 
between  the  molecules  (acquired  in  opposition  to  the  molecular 
forces  acting),  and  a  consequent  increase  in  their  potential 
energy  corresponds  within  the  substance,  to  the  change  of  state 
at  constant  temperature  as  observed  on  the  outside. 

It  must  be  understood  that  there  is  really  but  one  kind  of 
heat,  and  that  this  division  into  sensible  and  latent  is  only  a 
matter  of  convenience  in  order  to  signify  the  particular  energy 
change  which  is  effected  within  the  body.  The  heat  required 
to  raise  the  temperature  of  a  body  or  to  increase  its  sensible 
heat  is  thus  expended  in  increasing  the  velocity  of  the  molecules 
of  the  body,  and  hence  in  increasing  their  kinetic  energy.  The 
heat  required  to  effect  a  change  of  state,  or  to  increase  the 
potential  energy  is  expended,  on  the  other  hand,  in  increasing 
the  average  distance  between  the  molecules, and  in  increasing  the 
volume,  of  the  body  against  whatever  external  forces  may  exist. 

The  gradual  expansion  of  a  body  with  increase  of  tempera- 


442  PRACTICAL  MARINE  ENGINEERING. 

ture  is  accounted  for  by  assuming  that  as  the  velocity  of  the 
molecules  is  increased,  their  average  path  is  increased  also,  and 
hence  their  average  distance  apart,  and  hence  the  volume  of  the 
body. 

(3)  Temperature. — We   have   seen   above   that   temperature 
refers  to  the  condition  of  a  body  as  regards  its  sensible  heat,  or 
the  kinetic  energy  of  its  molecules.    Two  bodies  are  said  to  be 
at  the  same  temperature  when  there  is  no  tendency  for  heat  (that 
is,  molecular  energy)  to  flow  from  one  to  the  other.    This  con- 
dition is  measured  by  the  thermometer,  an  instrument  too  well 
known  to  require  particular  description. 

The  Fahrenheit  scale  which  is  commonly  used  by  engineers 
in  the  United  States  is  graduated  as  follows :  The  temperature 
of  melting  ice  is  called  32°  and  that  of  boiling  water  212°.  The 
interval  between  the  two  is  then  evenly  divided  into  180  parts, 
and  the  same  divisions  are  extended  above  and  below  as  far  as 
may  be  desired. 

On  the  Centigrade  scale  the  temperature  of  melting  ice  is 
called  o°  and  that  of  'boiling  water  100°.  The  interval  is  then 
evenly  divided  into  100  parts,  and  the  divisions  extended  above 
and  below  as  may  be  desired. 

For  transforming  temperatures  from  one  scale  to  the  other 
we  have  the  following  equations : 

F  ==  9/5  C  +  32° 

C  ==  5/9  (F  --  32°) 

where  F  and  C  denote  respectively  the  temperatures  on  the 
Fahrenheit  and  Centigrade  scales. 

Examples:    Transform  20°  C  into  Fah. 

Operation :  F  =:  9  x  20  -^  5  +  32  =  36  +  32  =  68°. 

Transform  20  Fah.  to  C. 

Operation:  C  =5  /9  (20  —  32)  —  5/9  (—  12)  -  -6  2/3° 
or  6  2/3°  below  zero. 

Transform  77  Fah.  into  C. 

Operation  :    C        =5/9   (77  —  32)   =  =  5/9  x  45  =  =  25° 

Transform  —  22°  Fah.  into  C. 

Operation  :   C  ==  5/9  (—  22  —  32)  ==  5/9  (—  54)  -      -  30° 

(4)  Heat  Unit. — Care  must  be  taken  to  distinguish  between 
quantity  of  heat  and  temperature.     The  first  refers  to  the  total 
amount  of  heat  energy  present  in  the  substance, the  second  to  the 
kinetic  energy  of  a  molecule.     A  large  cup  of  warm  water  and 


SPECIAL    TOPICS   AND   PROBLEMS.  443 

a  small  cup  of  hot  water  may  both  have  the  same  quantity  of 
heat,  but  not  the  same  temperature.  A  cup  of  hot  water  and  a 
barrel  full  of  hot  water  may  have  the  same  temperature,  but  the 
quantities  of  heat  will  be  very  different. 

For  measuring  quantities  of  heat,  use  is  made  of  a  heat  unit 
defined  as  the  amount  or  quantity  of  heat  required  to  raise  one 
pound  of  water  one  degree  in  temperature.  Inasmuch,  further- 
more, as  the  amount  thus  required  would  vary  slightly  at  different 
temperatures,  it  is  necessary  to  fix  the  temperature  at  which  the 
unit  is  to  be  defined.  The  temperature  thus  taken  for  the 
definition  of  the  heat  unit  has  sometimes  been  at  the  freezing 
point,  or  again  at  the  point  of  maximum  density  of  water  which 
is  about  39°  Fah.,  or  again  at  about  62°,  or  from  62°  to 
63°.  It  is  very  difficult  to  determine  the  amount  of  heat  required 
to  raise  water  one  degree  at  or  near  the  freezing  point,  while 
between  60°  and  70°,  or  at  about  an  average  atmospheric  tem- 
perature, the  measurements  are  most  readily  made.  For  this 
reason  a  temperature  within  this  range  is  to  be  preferred  for 
definition  of  the  heat  unit.  . 

The  heat  unit  thus  defined  is  often  known  as  the  British 
Thermal  Unit,  the  name  being  usually  abbreviated  to  B.  T.  U. 

(5)  Joule's  Equivalent. — Since  heat  is  but  a  form  of  energy 
it  follows  that  it  should  be  possible  to  transform  heat  into  me- 
chanical work,  and  vice  versa.  It  is  for  the  first  purpose  that 
the  steam  engine  is  used,  while  instances  of  the  latter  transforma- 
tion are  constantly  before  our  eyes,  as  in  the  heat  developed 
by  the  friction  of  a  bearing,  or  in  turning  a  chip  from  a  bar  of 
steel,  etc. 

It  therefore  becomes  of  importance  to  know  the  ratio  of 
transformation,  or  how  much  mechanical  work  measured  in 
foot-pounds  corresponds  to  one  heat  unit  as  above  defined.  This 
has  been  made  the  subject  of  careful  experiment  extending  over 
the  past  one  hundred  years,  and  the  latest  and  most  reliable 
results  seem  to  give  for  this  ratio  the  value  778.  That  is,  one 
B.  T.  U.  is  equivalent  to  778  foot  pounds  of  mechanical  work. 
This  means  that  when  in  a  steam  or  other  heat  engine  heat  is 
transformed  into  mechanical  work,  for  every  B.  T.  U.  so  trans- 
formed and  disappearing  as  heat,  778  foot  pounds  of  work  will 
be  obtained ;  or  again  when  mechanical  work  is  transformed  into 
heat,  for  every  778  foot  pounds  so  transformed  and  disappear- 
ing as  work,  one  B.  T.  U.  of  heat  will  appear. 


444  PRACTICAL  MARINE  ENGINEERING. 

This  number  or  ratio,  778,  is  known  as  the  mechanical 
equivalent  of  heat,  or  frequently  as  Joule's  equivalent,  though 
its  value  as  determined  by  Joule  was  somewhat  smaller  than  the 
value  given  above. 

(6)  Transfer  of  Heat. — Heat  may  be  transferred  from  one 
body  or  place  to  another  in  three  different  ways :  by  radiation, 
by  conduction,  and  by  convection. 

By  radiation  we  mean  the  transfer  of  heat  through  space  in 
straight  lines,  as  from  the  sun  to  the  earth,  or  from  a  furnace  fire 
to  the  face  when  the  door  is  opened. 

By  conduction  we  mean  the  transfer  of  heat  along  a  body 
from  one  molecule  to  the  next,  as  when  a  slice  bar  becomes 
warm  at  one  end  if  red-hot  at  the  other. 

By  convection  we  mean  the  transfer  of  heat  from  one  point 
of  a  liquid  or  gas  to  another  by  means  of  currents  set  up  in  the 
liquid  or  gas  and  carrying  the  heated  molecules  from  one  place 
to  another,  as  in  the  circulation  set  up  within  a  Scotch  boiler. 

Two  other  operations  are  also  concerned  in  the  transfer  of 
heat  from  one  substance  to  another.  These  are  emission  and 
absorption. 

By  emission  we  mean  the  giving  off  or  transfer  of  heat  from 
the  molecules  of  one  body  to  those  of  another.  By  absorption  we 
mean  the  converse  of  this,  the  receiving  of  heat  by  the  molecules 
of  one  body  from  those  of  another. 

•The  heating  of  water  in  a  boiler  is  due,  at  least  in  part,  to 
all  of  these  processes.  The  fire  in  the  furnace  radiates  heat  to 
the  crown  sheet ;  convection  and  draft  currents  convey  the  hot 
gas  to  the  heating  surface ;  there  is  emission  from  the  hot  gases 
and  absorption  by  the  metal  of  the  heating  surfaces;  there  is 
conduction  through  the  metal  from  the  fire  to  the  water  side ; 
there  is  emission  from  the  metal  and  absorption  by  the  water; 
and  finally  there  are  convection  currents  developed  in  the  water 
by  means  of  which  the  temperature  is  more  or  less  uniformly 
raised. 

[3]  Steam. 

Steam  or  the  vapor  of  water  is  the  substance  almost  univer- 
sally used  as  the  medium  through  which  the  heat  set  free  by 
the  coal  is  transformed  into  the  mechanical  work  of  the  engine 
or  pump.  Its  properties  are  therefore  of  great  importance  for 
the  engineer,  and  we  may  properly  study  briefly  the  more  im- 
portant at  this  point. 


SPECIAL    TOPICS   AND    PROBLEMS. 


445 


(i)  Formation  of  Steam. — Let  AB  in  Fig.  276  be  a  very  tall 
vessel  open  at  the  top  and  having  an  inside  cross-section  of  one 
square  inch.  Let  us  suppose  at  the  start  that  there  is  in  the  bot- 
tom of  this  vessel  one  cubic  inch  of  water  at  say  60°  temperature. 
On  top  of  the  water  let  there  be  a  piston  as  shown  which  we 
may  suppose  to  move  without  friction,  and  to  be  without  weight. 
In  other  words  we  wish  simply,  something  to  separate  the  water 
from  the  air.  Then  on  the  surface  of  the  water  there  will  be  just 
the  atmospheric  pressure  of  say  14.7  pounds  per  square  inch. 
Now  let  heat  be  applied  at  the  bottom  of  the  chamber.  The  first 


11 


Fig.  276.    The  Formation  of  Steam. 

result  will  be  a  transfer  of  heat  through  into  the  water,  and  a 
resultant  rise  in  temperature  of  the  water  near  the  heating  sur- 
face. In  consequence  of  this  the  water  will  expand  somewhat  and 
thus  become  lighter  than  the  other  water  above  and  farther  from 
these  surfaces.  The  heated  water  will  thus  tend  to  rise  to  the 
top  and  so  displace  the  cooler  water  there,  which  will  in  conse- 
quence sink  and  thus  in  turn  be  brought  into  contact  with  the 
heating  surfaces.  There  is  set  up  in  this  way  a  general  ascend- 
ing current  of  warmer  water  and  a  corresponding  descending 
current  of  cooler  water  by  means  of  which  the  whole  mass  is 
gradually  raised  in  temperature. 

In  this  manner  are  formed  the  convection  currents  referred 


446  PRACTICAL  MARINE  ENGINEERING. 

to  in  the  preceding  section,  and  to  their  formation  in  a  steam 
boiler  is  due  the  circulation  of  the  water,  especially  in  those  of 
the  fire-tube  or  tank  type. 

In  this  way  then  the  temperature  of  the  water  will  gradually 
rise  until  it  reaches  212°.  The  temperature  then  ceases  to  rise 
and  steam  begins  to  form,  rapidly  increasing  the  volume  belowr 
the  piston  and  thus  forcing  it  upward.  The  steam  formed  is  of 
the  same  temperature,  212°,  as  the  water  of  which  it  is  formed, 
the  only  changes  being  the  increase  of  volume  and  the  change 
of  state.  If  we  continue  to  supply  heat  at  the  bottom  and  pre- 
vent its  escape  from  the  sides  of  the  tube  or  chamber,  the  water 
will  thus  gradually  be  all  converted  into  steam,  just  balancing 
by  its  own  pressure  the  atmospheric  pressure  on  the  top  of  the 
piston.  The  volume  of  steam  thus  formed  would  be  1,663  cubic 
inches,  or  in  other  words  the  tube  would  have  to  be  1,663  inches 
or  138.6  feet  high  to  allow  of  the  operation  as  we  have  supposed 
it  to  take  place. 

Suppose  now  that  at  the  beginning  the  piston  is  loaded  down 
with  a  weight  so  that  the  total  load  on  the  water  is  20  pounds 
instead  of  14.7.  Then  let  heat  be  supplied  as  before.  A  like 
series  of  changes  will  follow,  but  the  water  instead  of  beginning 
to  change  state  from  liquid  to  vapor  at  212°  must  be  heated  to 
228°  before  the  change  begins,  while  the  final  volume  will  be 
only  1,244  cubic  inches.  If  the  initial  pressure  were  100  pounds 
then  the  temperature  at  which  the  change  of  state  would  begin 
would  be  328°,  and  the  final  volume  would  be  only  275  cubic 
inches.  Similarly  for  200  pounds  pressure,  the  figures  are  382° 
and  144  cubic  inches. 

On  the  other  hand,  if  by  means  of  an  air  pump  the  pressure 
on  the  water  were  decreased  below  that  of  the  atmosphere  the 
temperature  of  change  would  become  lower,  and  the  volume 
greater.  Thus  if  the  pressure  is  10  pounds  the  figures  are  193° 
and  2,385  cubic  inches,  and  if  5  pounds  they  are  162°  and  4,576 
cubic  inches.  Similarly,  to  boil  water  at  32°,  or  the  freezing 
point,  it  would  be  necessary  to  reduce  the  pressure  to  .089 
pounds,  while  the  volume  of  vapor  formed  would  be  about  21,170 
cubic  inches. 

In  general  we  thus  find  that  as  the  pressure  is  increased  or 
decreased  there  is  a  corresponding  rise  or  fall  in  the  tempera- 
ture at  which  the  formation  of  vapor  begins,  and  that  it  re- 
mains fixed  at  this  temperature  during  the  process  of  change  of 


SPECIAL   TOPICS   AND   PROBLEMS.  447 

state,  and  that  the  temperature  of  the  vapor  formed  is  also  the 
same  as  that  of  the  water  from  which  it  is  formed. 

It  thus  appears  that  steam  is  simply  the  vapor  of  water, 
or  water  in  the  vaporous  state,  as  defined  in  [2].  The 
process  of  steam  formation  as  above  described  is  known  as 
boiling  or  ebullition,  or  sometimes  in  the  general  sense  as  vapor- 
ization. The  temperature  at  which  the  change  of  state  occurs  is 
known  as  the  boiling  point  or  point  of  ebullition. 

At  lower  temperatures  there  is  always  a  certain  amount  of 
slow  vaporization  going  on,  the  pressure  of  the  vapor  formed 
being  limited  to  that  corresponding  to  the  temperature  of  the 
water.  It  is  by  means  of  such  slow  vaporization  that  water  is 
carried  up  for  the  formation  of  rain  clouds  from  the  surfaces  of 
rivers,  lakes  and  oceans,  or  that  mud  dries  up  in  the  roads,  or 
clothes  when  hung  out  to  dry.  Thus  if  the  temperature  is  100° 
the  maximum  vapor  pressure  is  about  one  pound.  Considerable 
vapor  will  thus  be  formed,  which  will  gradually  find  its  way  up- 
ward into  the  air,  at  least  so  long  as  the  air  is  not  saturated ;  i.e., 
already  charged  with  vapor  of  the  full  pressure  corresponding  to 
the  temperature.  This  is,  however,  a  branch  of  the  subject  that 
we  cannot  here  pursue  further. 

When,  however,  the  temperature  is  such  that  the  vapor 
pressure  is  sufficient  to  just  balance  the  entire  pressure  on  the 
surface  of  the  liquid,  then  the  vapor  is  formed  with  freedom,  and 
more  or  less  from  the  body  of  the  liquid,  producing  the  agitation 
and  other  conditions  which  constitute  boiling  or  ebullition  as  re- 
ferred to  above. 

We  have  thus  examined  in  some  detail  the  formation  of 
steam  at  constant  pressure.  Let  us  next  examine  briefly  its  for- 
mation at  constant  volume,  the  case  which  corresponds  to  its 
generation  in  a  steam  boiler. 

The  boiler  being  first  open  to  the  air  through  the  safety 
valve,  the  water  is  subject  simply  to  atmospheric  pressure.  The 
heating  of  the  water  and  first  formation  of  steam  proceed  accord- 
ing to  the  process  as  described  above.  The  air  is  thus  displaced 
from  the  boiler  and  driven  out  through  the  safety  valve  or  other 
escape.  The  safety  valve  or  escape  is  then  closed  and  in  con- 
sequence the  steam  which  is  formed  tends  to  increase  the  pres- 
sure, and  as  this  rises  the  temperature  of  the  boiling  point  will 
rise  also.  In  this  way  as  heat  is  added,  a  part  of  it  is  used  in 
raising  the  temperature  of  the  water  and  steam  up  to  the  ever- 


448  PRACTICAL  MARINE  ENGINEERING. 

rising  boiling  point,  while  the  remainder  goes  for  the  vaporiza- 
tion of  a  fresh  portion  of  steam.  In  this  way  the  volume  of  vapor 
remains  practically  constant,  but  the  pressure  and  temperature 
rise  together  according  to  the  regular  law  which  relates  the  one 
to  the  other,  while  the  increase  of  vapor  is  accommodated  in 
the  constant  volume  by  the  increase  in  density,  or  decrease  in 
volume  required  per  pound  as  the  pressure  rises. 

It  is  thus  seen  that  the  temperature  and  volume  of  steam 
are  closely  dependent  on  the  pressure  to  which  it  is  subjected. 

For  engineering  purposes  pressure  may  be  measured  from 
two  different  starting  points.  The  true  or  so-called  absolute 
pressure  is  measured  from  the  zero  or  no-pressure  condition,  and 
is  the  true  or  total  pressure  exerted  by  the  gas  or  vapor  in  ques- 
tion. The  ordinary  steam  gauge,  however,  as  described  in  Sec. 
17  [7]  does  not  measure  the  absolute  pressure,  but  simply  the 
difference  between  this  and  the  pressure  of  the  atmosphere.  This 
is  due  to  the  fact  that  the  gauge  is  subjected  to  the  pressure  of 
the  steam  on  one  side  of  the  tube  and  to  that  of  the  atmosphere 
on  the  other  side.  It  thus  measures  simply  the  difference  be- 
tween the  two.  This  is  commonly  called  "gauge  pressure."  The 
absolute  pressure  is  greater  than  the  gauge  pressure  therefore, 
by  the  pressure  of  the  atmosphere.  This  varies  with  the  altitude 
and  with  other  circumstances  affecting  the  barometer.  For  en- 
gineering purposes  it  is  very  commonly  taken  at  15  pounds  per 
square  inch.  A  more  correct  average  for  the  sea  level  is,  how- 
ever, 14.7,  as  noted  above.  It  results  therefore  that  having  given 
the  gauge  pressure  we  may  find  the  absolute  pressure  by  adding 
15  or  14.7,  as  we  may  choose,  according  to  the  degree  of  ac- 
curacy needed  in  the  case  in  hand. 

(2)  Saturated  and  Superheated.  Steam. — When  steam  and 
water  are  present  in  the  same  vessel  together  and  there  is  no 
tendency  for  the  water  to  change  into  steam  or  the  steam  into 
water  except  as  heat  is  added  or  taken  away,  the  water  and  the 
steam  are  said  to  be  in  thermal  equilibrium.  When  steam  is  thus 
in  equilibrium  in  contact  with  water,  it  is  said  to  be  saturated. 
Thus  during  the  entire  process  of  steam  formation  illustrated  in 
Fig.  276,  the  steam  is  saturated. 

When  there  is  no  moisture  or  water  in  the  liquid  condition 
suspended  in  or  mixed  with  the  vapor,  the  steam  is  said  to  be  'dry. 

When  there  is  moisture  or  water  suspended  in  or  mixed 
with  the  vapor,  the  steam  is  said  to  be  moist  or  wet.  In  such  case 


SPECIAL    TOPICS   AND   PROBLEMS.  449 

the  steam  or  vapor  part  of  the  mixture  must  itself  be  in  the 
saturated  condition  as  defined  above,  so  that  wet  steam  is  simply 
a  mixture  of  saturated  water  vapor  and  liquid  water. 

When  steam  is  free  from  all  suspended  moisture,  but  is  still 
in  the  saturated  condition  as  determined  by  its  pressure,  tem- 
perature and  volume,  it  is  called  dry  and  saturated.  Thus  the 
condition  of  the  steam  in  the  vessel  of  Fig.  276,  just  as  the  last 
bit  of  vapor  is  formed,  is  dry  and  saturated.  During  the  opera- 
tion the  vapor  would  be  dry  and  saturated  provided  it  contained 
no  suspended  moisture.  Practically  this  is  a  condition  difficult 
to  realize.  The  greater  or  less  violence  of  the  ebullition  is  apt 
to  carry  up  a  certain  amount  of  water  in  the  shape  of  fine  mist 
into  the  steam  space,  from  which  it  settles  back  only  slowly,  and 
so  is  liable  to  be  carried  over  into  the  engine.  The  steam  fur- 
nished by  the  average  boiler  under  good  conditions  contains 
usually  not  less  than  from  I  to  2,  per  cent,  of  moisture,  while 
under  poor  conditions  the  amount  may  rise  to  5  per  cent,  and 
more. 

Suppose  now,  referring  to  Fig.  276,  that  after  the  last  bit  of 
water  has  been  vaporized,  heat  is  still  further  applied,  the  pres- 
sure on  the  piston  remaining  the  same.  The  temperature  which 
during  the  process  of  vaporization  has  remained  stationary,  will 
now  begin  to  rise,  accompanied  also  by  an  increase  of  volume. 

If  we  now  recall  the  three  stages  which  the  water  has  passed 
through,  all  at  constant  pressure,  it  appears  that  during  the  first 
stage  there  was  a  rise  in  temperature  of  the  water  at  nearly  con- 
stant volume :  during  the  second  stage  (that  of  steam  formation) 
there  was  an  increase  of  volume  at  constant  temperature :  during 
the  third  stage,  as  just  described,  there  is  increase  of  both  volume 
and  temperature. 

If  in  this  last  operation  instead  of  keeping  the  pressure  con- 
stant the  piston  were  held  fast,  thus  keeping  the  volume  con- 
stant, we  should  find  with  the  addition  of  heat  that  both  the  tem- 
perature and  the  pressure  would  increase. 

Steam  in  the  condition  resulting  from  these  operations  is 
said  to  be  superheated.  As  compared  with  saturated  steam  its 
temperature  and  volume  are  greater  for  the  same  pressure,  or  its 
temperature  and  pressure  are  greater  for  the  same  volume,  or 
its  volume  is  greater  and  pressure  less  at  the  same  temperature. 
It  is  clear  that  superheated  steam  cannot  be  in  contact  with 
water  and  remain  superheated.  It  cannot  therefore  be  moist. 


450  PRACTICAL  MARINE  ENGINEERING. 

If  it  were  brought  into  contact  with  water  it  would  lose  its  super- 
heat and  become  saturated,  forming  by  the  heat  given  up,  a 
little  more  vapor  from  the  water  present. 

We  may  also  put  the  relation  between  saturated  and  super- 
heated steam  into  the  following  form  : 

Saturated  steam  contains  only  as  much  heat  as  absolutely 
necessary  for  its  maintenance  as  steam  at  the  given  pressure. 
Superheated  steam  at  the  same  pressure  contains  more  heat  than 
saturated. 

The  temperature  and  volume  per  pound  for  saturated  steam 
correspond  with  the  pressure  as  in  the  process  of  vaporization, 
and  are  respectively  the  lowest  temperature  and  smallest  volume 
at  which  steam  of  the  given  pressure  can  exist.  The  temperature 
and  volume  per  pound  lor  superheated  steam  are  both  larger 
for  the  same  pressure  than  for  saturated  steam. 

[4]  Xotal  Heat  in  a  Substance. 

(i)  Total  Heat  of  Steam. — The  total  heat  of  a  body  in  a  given 
condition  is  the  total  amount  of  heat  required  to  produce  this 
condition,  reckoning  from  some  starting  point  agreed  upon.  For 
steam  this  point  is  usually  taken  as  32°  Fah.,  or  the  freezing 
point  of  water.  The  total  heat  per  pound  of  steam  at  a  given 
pressure  and  temperature,  means  then  the  total  amount  of  heat, 
both  sensible  and  latent,  required  to  produce  one  pound  of  steam 
of  the  given  pressure  and  temperature,  from  water  at  32°.  These 
quantities  of  heat  are  used  in  the  solution  of  problems  relating 
to  the  heat  required  for  evaporation,  boiler  efficiency,  gain  by 
feed-water  heating,  etc.  The  value  of  the  total  heat  in  terms  of 
the  temperature  is  very  closely  given  by  the  following  approxi- 
mate equation : 

H  =  1082  +  .3* 
while  the  latent  heat  is  similarly  given  by  the  equation  : 

L  =  1114  —  .ft. 

In  these  equations,  H  denotes   the  total  heat,  L  the  latent 
heat,  and  t  the  temperature. 

Instead  of  using  these  or  other  similar  equations,  the  values 
are  more  conveniently  taken  from  tables  prepared  so  as  to  give 
the  various  quantities  for  regularly  varying  values  of  the  pres- 
sure. Thus  from  the  Table  it  appears  that  at  14.7  pounds 
pressure  absolute,  or  at  the  pressure  of  the  atmosphere, 
it  requires  180.9  B.  T.  U.  to  heat  the  water  from  32°  to  the  boil- 


SPECIAL    TOPICS   AND   PROBLEMS.  451 

ing  point  212°,  and  then  965.7  B.  T.  U.  to  completely  vaporize 
it  at  this  point.  The  great  excess  of  the  latter  or  latent  heat  over 
the  former  or  sensible  heat  may  thus  be  noted.  It  is  also  seen 
that  according  to  the  table  the  heat  required  to  raise  the  water 
from  32°  to  212°  is  not  exactly  measured  by  the  difference  in 
degrees  which  is  180.  The  excess  is  due  to  the  fact  that  the 
B.  T.  U.  is  defined  for  i°  rise  from  62°  to  63°,  while  the  amount 
required  to  make  i°  difference  at  other  temperatures  is  slight- 
ly different,  increasing  on  the  whole  for  higher  tempera- 
tures, so  that  between  32°  and  212°  the  average  is  slightly 
greater  than  from  62°  to  63°.  It  thus  results  that  the  sensible 
heat  per  pound  of  water  involved  in  a  temperature  change  is' 
slightly  greater  than  the  number  of  degrees  which  measures 
such  change.  This  difference  is,  however,  so  small  that  for  most 
engineering  purposes  it  may  be  neglected  if  more  convenient, 
and  the  number  of  heat  units  per  pound  of  water  may  be  taken 
equal  to  the  number  of  degrees  difference  in  temperature. 

(2)  Total  Heat  of  a  Mixture  of  Steam  and  Water. — Steam  as 
actually  used  is  usually  moist ;  that  is,  it  contains  a  small  fraction 
of  water.  To  find  how  much  heat  is  required  to  produce  one 
pound  of  such  a  mixture  of  steam  and  water,  a  given  fraction 
being  steam  and  the  remainder  water,  we  have  simply  to  re- 
member that  all  of  the  water  must  be  raised  to  the  temperature 
of  boiling,  while  only  the  given  fraction  is  vaporized.  If  there- 
fore S  denotes  the  sensible  heat  and  L  the  latent  heat,  while 
x  is  the  fraction  which  Is  steam,  or  the  quality  of  the  steam  as 
it  is  called,  then  the  heat  H  required  to  produce  one  pound  of 
the  mixture  will  be  : 

H  —  S  -f-  xL. 

The  quality  ,r  -is  usually  expressed  on  the  percentage  basis. 
The  following  examples  will  illustrate  the  use  of  the  steam 
tables : 

(1)  Find  the  sensible  heat,  the  latent  heat  and  the  total  heat 
in  one  pound  of  steam  at  120  pounds  gauge  pressure.* 

Ans.  from  the  table,  322.1,  866.6,  1188.7. 

(2)  Find  the  heat  in  i  pound  of  feed  water  at  a  temperature 
of  110°. 

Ans.  no  —  32  =  78. 

*  For  present  purposes,  and  in  the  following  problems,  it  will  be  suffi- 
ciently accurate  to  take  the  pressure  of  the  atmosphere  as  15  pounds  per 
square  inch.  The  absolute  pressure  is  therefore  found  from  the  gauge 
pressure  by  simply  adding  15. 


452  PRACTICAL  MARINE  ENGINEERING. 

(3)  How  much  heat  would  be  required  to  produce  the  steam 
in  example  (i)  from  the  feed  water  in  (2)? 

Ans.  The  difference  between  the  two  or  1110.7. 

Remark:  These  three  examples  show  how  we  may  find  the 
heat  necessary  to  produce  a  pound  of  steam  of  given  pressure 
from  feed  water  of  any  given  temperature. 

(4)  How  much  heat  is  required  to  make  i  pound  of  steam 
at  150  pounds  gauge  pressure  from  feed  water  at  130°? 

Ans.  1095.5. 

(5)  How  much  heat  is  required  to  produce  i  pound  of  moist 
steam  of  92  per  cent,  quality  at  150  pounds  gauge  pressure  from 
feed  water  at  120°? 

Solution : 

The  sensible  heat  per  pound  of  steam  is.  ...   338.4 
The  sensible  heat  per  pound  of  feed  is 88.0 

The  difference  is 250.4 

The  latent  heat  for  one  pound  is  855.1.    But  since  only  92 

per  cent,  is  vaporized,  only  .92  of  this  will  be  required.    We  have 

therefore : 

H  =  5  +  xL  —  250.4  +  .92  X  855.1  =  1037.    Ans. 

(6)  One  engine  requires  per  I.H.P.  per  hour,   16  pounds 
of  steam  of  96  per  cent,  quality  at  150  pounds  gauge  pressure, 
the  feed  being  at  a  temperature  of  140°.  Another  engine  requires 
20  pounds  of  steam  of  90  per  cent,  quality  at  no  pounds  gauge 
pressure,  the  feed  being  at  a  temperature  of  110°. 

Find  the  amounts  of  heat  required  per  hour  in  the  two  en- 
gines, and  hence  their  real  comparison  as  heat  engines. 

By  the  methods  illustrated  above  we  find  as  follows : 

For  the  first  engine  16821  B.  T.  U.  per  hour. 

For  the  second  engine  20436  B.  T.  U.  per  hour. 

The  second  engine  requires  therefore  3615  B.  T.  U.  per 
hour  more  than  the  first,  and  in  consequence  is  about  21.5  per 
cent,  more  expensive  in  terms  of  the  heat  required. 

Further  illustrations  of  these  principles  will  be  found  in 
Sec.  58. 

[5]  I/atent  Heat  in  Passing  from  Ice  to  Water. 

We  have  seen  in  [2]  (i)  that  a  certain  amount  of  heat  is 
absorbed  in  the  melting  of  ice  at  the  constant  temperature  of  32°. 
It  is  thus  rendered  latent  or  is  taken  up  in  effecting  the  change 
of  state  in  the  same  general  manner  that  heat  is  rendered  latent 


SPECIAL    TOPICS   AND   PROBLEMS.  -45* 

in  passing  from  liquid  to  vapor.    It  may  be  of  value  to  note  here 
the  quantity  of  heat  thus  rendered  latent. 

This  amounts  to  about  143  heat  units,  or  B.  T.  U.,  per  pound 
of  ice  melted  from  32°  into  water  at  the  same  temperature. 

Sec.  58.  ST£AM  BOH,ER  ECONOMY. 

[i]  General  Principles. 

There  may  be  several  different  bases  for  boiler  economy  ac- 
cording to  the  particular  feature  held  in  especial  prominence. 
The  output  of  the  boiler  is  estimated  in  terms  of  the  steam  pro- 
duced, and  we  may  have  the  following  kinds  of  economy : 

(1)  Economy  in  coal  consumption,  increasing  with  the  out- 
put of  steam  per  pound  of  coal  burned. 

(2)  Economy  in  weight  of  boiler,  increasing  with  the  output 
of  steam  per  pound  of  boiler. 

(3)  Economy  in  first  cost,  increasing  with  the  output   of 
steam  per  dollar  invested  in  the  boilers. 

(4)  Economy  of  maintenance  or  total  life,  increasing  as  the 
life  .of  the  boiler  is  longer  and  the  amount  necessary  for  repairs 
is  smaller. 

It  is  never  possible  to  fulfil  in  the  highest  degree  the  condi- 
tions for  these  various  kinds  of  economy,  and  a  compromise  must 
always  be  made  among  them,  though  usually  (i)  or  (2)  will  take 
the  first  place  in  the  order  of  importance. 

Without  special  note,  however,  the  term  economy  is  under- 
stood to  refer  to  (i),  though  the  considerations  relating  to  the 
others  should  always  be  kept  in  mind.  In  some  cases,  as  in  tor- 
pedo boat  and  like  practice,  (2)  may  assume  first  place  in  the 
order  of  importance,  and,  perhaps,  require  some  sacrifice  relative 
to  the  others.  We  will  now  consider  more  especially  the  econ- 
omy referred  to  under  (i). 

From  the  standpoint  of  coal  economy  or  efficiency,  the 
boiler  is  charged  with  all  the  coal  that  is  thrown  through  the 
furnace  doors,  and  is  credited  with  the  steam  which  it  sends  to 
the  engine.  Or  to  state  the  matter  more  definitely,  it  is  charged 
with  all  the  heat  which  could  be  gotten  from  this  coal  by  perfect 
and  complete  combustion,  and  is  credited  with  the  heat  which  is 
transferred  through  and  actually  used  in  the  formation  of  steam. 
If  the  efficiency  were  perfect,  or  if  there  were  no  loss,  these  two 
amounts  of  heat  would  be  equal.  Actually  there  are  many  losses, 
large  and  small,  and,  in  consequence,  the  latter  is  considerably 


454  PRACTICAL  MARINE  ENGINEERING. 

less  than  the  former.  The  ratio  of  the  two  is  known  as  the  boiler 
efficiency.  In  practice  its  value  varies  from  50  to  75  or  80  per 
cent.  Following  are  the  more  important  sources  of  loss  which 
occasion  this  drop  in  efficiency. 

In,,  jthe  first  place,  a  little  of  the  fuel  may  fall  unburned 
through  the  grate  into  the  ash  pit.  Again,  a  little  in  the  form  of 
dust  and  small  bits  may  be  carried  by  a  strong  draft,  either  un- 
burnt  gr  only  partially  burnt,  through  into  the  tubes,  uptakes  or 
funnel.  Still  another  small  portion  may  escape  as  srnoke,  which 
consists  almost  entirely  of  very  fine  particles  of  unburnt  carbon 
formed  from  the  gases  which  are  distilled  away  from  the  coal  in 
the  process  of  combustion.  Still  another  portion  of  these  gases 
may  escape  unchanged  and  unconsumed.  Again,  there  may  be 
an  incomplete  combustion  of  the  carbon  forming  carbon  monoxide, 
and  giving  only  about  4,450  heat  units  per  pound,  instead  of 
14,500  which  result  from  the  complete  combustion  into  carbon 
dioxide.  Hence,  whatever  carbon  escapes  in  the  form  of  carbon 
monoxide  is  only  partly  burned,  and  may  be  considered  as  car- 
rying away  over  two-thirds  of  the  heat  which  would  be  liberated 
by  complete  combustion.  These  losses  all  occur  in  the  furnace, 
and  are  due  to  poor  firing  and  to  imperfect  combustion. 

To  reduce  them  to  the  lowest  limit,  the  fireman  must  know 
his  business,  and  be  willing  to  attend  to  it  with  ceaseless  care 
and  diligence.  In  addition,  there  must  be  provided,  by  proper 
design,  the  necessary  supply  of  air  both  above  and  below  the 
grate,  together  with  such  arrangements  as  experience  may  show 
are  needed  for  good  combustion  with  the  fuel  in  hand.  At  best 
this  loss  may  be  reduced  to  perhaps  2  or  3  per  cent.,  while  with 
carelessness  or  poor  design,  or  both,  it  may  easily  reach  values 
from  10  to  20  per  cent. 

The  heat  being  thus  more  or  less  perfectly  liberated- in  the 
furnace,  is  then  passed  on  to  the  boiler  heating  surface,  whose 
duty  it  is  to  transfer  it  through  into  the  water  on  the  other  side. 
The  energy  is  still  to  exist  as  heat,  but  it  is  to  be  transferred  from 
the  hot  gas  to  the  water,  thus  converting-  the  latter  into  steam. 
This,  however,  cannot  be  perfectly  accomplished,  and  thus  arises 
a  further  loss.  A  part  of  the  heat,  instead  of  passing  through  the 
heating  surface,  goes  up  the  funnel  carried  bv  the  escaping  gases, 
and  so  gets  away  into  the  outside  air.  Another  and  smaller  part 
escapes  by  radiation  into  the  fire  room.  These  losses  it  is  im- 
possible wholly  to  avoid.  It  would  be  necessary  to  avoid  all  loss 


SPECIAL    TOPICS   AND   PROBLEMS.  455 

of  heat  by  radiation,  and  to  reduce  the  temperature  of  the  pro- 
ducts of  combustion  in  the  funnel  to  that  of  the  outside  air.  The 
latter,  especially,  cannot  be  done  for  the  best  of  reasons.  In 
the  first  place,  the  temperature  cannot  be  reduced  below  that  of 
the  steam  and  water  in  the  boiler,  because  heat  always  flows 
naturally  from  a  hot  body  to  a  cooler  one,  and  it  will,  therefore, 
flow  from  the  gas  to  the  water  only  so  long  as  the  latter  is  the 
cooler  of  the  two.  The  actual  temperature  of  the  escaping  gases 
must  be  considerably  higher  than  that  of  the  steam,  because  in 
the  first  place  sufficient  heating  surface  to  reduce  them  to  nearly 
the  same  temperature  could  hardly  be  allowed ;  and,  again,  aside 
from  blowers,  the  strength  of  draft  is  dependent  on  the  tempera- 
ture of  the  hot  gas  in  the  funnel,  and  for  a  satisfactory  rate  of 
combustion  it  is  necessary  to  discharge  the  products  of  combus- 
tion at  temperatures  not  less  than  500  to  600  degrees.  This  loss 
is  one  therefore  which  exists  in  the  nature  of  things,  and  cannot 
be  reduced  below  some  20  or  30  per  cent. 

On  the  whole,  then,  the  entire  losses  under  the  best  condi- 
tions can  hardly  be  reduced  much  below  25  per  cent.,  while  wi  h 
poor  conditions  they  may  aggregate  40  to  50  per  cent.  The 're- 
maining fraction,  or  the  50  to  75  or  80  per  cent.,  represents  then 
the  efficiency  of  the  boiler  as  defined  above. 

Since  a  pound  of  average  good  coal  has  available  sor-e 
13,000  to  14,000  heat  units,  it  follows  that  the  heat  actually 
utilized  per  pound  of  coal  is  usually  found  between  say  7,000  and 
11,000  units. 

In  general  the  conditions  favorable-  to  high  efficiency  are 
the  following: 

(1)  A  free  burning  coal  of  good  quality,  with  suitable  fur- 
naces and  air  supply  for  complete  combustion. 

(2)  Moderate  draft. 

(3)  Abundant  heating  surface. 

Or,  as  a  combination  of  (2)  and  (3),  we  may  put : 
(2)  Moderate  evaporation  required  per  square  foot  of  heat- 
ing surface. 

The  opposite  of  these  conditions  will  cause  necessarily  a  loss 
in  efficiency  more  or  less  pronounced  according  to  circumstances. 

[2]  Evaporation  Per  Pound  of  Coal. 

The  efficiency  of  a  boiler  is  often  roughly  estimated  by  the 
number  of  pounds  of  water  evaporated  into  steam  per  pound  of 


456  PRACTICAL  MARINE  ENGINEERING. 

coal  burned  on  the  grates.  This,  according  to  conditions,  may 
vary  from  6  or  7  to  perhaps  n.  Remembering  that  it  usually 
requires  rather  more  than  1,000  heat  units  per  pound  of  steam, 
the  general  agreement  between  these  figures  and  those  above  foi 
the  heat  utilized  per  pound  of  coal  is  readily  seen.  In  fact,  the 
figures  for  the  heat  utilized  are  derived  really  from  a  measure- 
ment of  the  pounds  of  steam  evaporated  per  pound  of  coal, 
together  with  a  knowledge  of  the  heat  required  per  pound  of 
steam,  the  latter  being  derived,  of  course,  from  the  conditions 
of  the  evaporation. 

When  we  remember  the  great  difference  in  the  amount  of 
heat  required  per  pound  of  steam,  depending  on  the  temperature 
of  the  feed,  the  temperature  of  the  steam,  and  whether  the  steam 
is  moist  or  dry,  it  is  clear  that  for  any  fair  measure  of  boiler  per- 
formance in  terms  of  steam  formed  per  pound  of  coal,  these 
differences  must  be  allowed  for,  especially  in  comparisons  be- 
tween boilers  -working  under  different  conditions. 

To  this  end  it  is  customary  to  reduce  the  number  of  pounds 
evaporated  to  what  it  would  be  if  the  steam  were  dry  and  the 
temperature  of  both  feed  and  steam  were  212  degrees.  In  such 
case  it  would  require  to  make  one  pound  of  steam  simply  the 
latent  heat  at  212  degrees,  or  966  B.  T.  U.  (British  thermal 
units). 

This  is  known  as  the  reduced  evaporation,  or  the  equivalent 
evaporation  from  and  at  212  degrees.  It  is  really  the  number  of 
pounds  of  steam  which  would  be  formed  if  each  required  966 
B.  T.  U.,  and  is,  therefore,  simply  a  measure  of  the  B.  T.  U.  put 
into  the  steam  per  pound  of  coal. 

The  ratio  between  the  number  of  B.  T.  U.  actually  required 
and  the  966  is  known  as  the  factor  of  evaporation.  These  factors 
are  often  arranged  in  tabular  form,  assuming  dry  steam  in  each 
case,  but  with  temperature  of  feed  water  and  steam  varying  over 
the  usual  rano-e. 

The  annli cation  of  these  various  principles  relating  to  boiler 
economy  will  be  better  understood  by  the  solution  of  the  follow- 
ing illustrative  problems.  In  these  problems  we  shall  still  for 
convenience  consider  the  pressure  of  the  atmosphere  as  15 
pounds  per  square  inch,  and  the  absolute  pressure  therefore  as 
15  pounds  greater  than  the  gauge  pressure. 

(i)  Temperature  of  feed  110°,  steam  pressure  150  pounds, 
gauge.  Thermal  value  of  the  coal  14,000  thermal  units  per 


SPECIAL   TOPICS   AND   PROBLEMS.  457 

pound.    Efficiency  of  boiler  .64.    Find  the  pounds  of  water  evap- 
orated into  dry  steam  per  pound  of  coal. 

Operation : 

From  the  steam  tables  : 

Heat  in  the  water  at  boiling  point 3384 

Heat  in  the  feed  =  1 10  —  32  = 78 

Difference    260.4 

Latent  heat 855.1 

Heat  required  per  pound  of  dry  steam IIT5-5 

Heat  available  per  pound  of  coal  =  .64  X  14,000  =  8,960. 

Hence  pounds  of  steam  evaporated  =  8960  -f-  1115.5  — 
8.03  Ans. 

(2)  Temperature  of  feed  140°.  Steam  pressure  200  pounds, 
gauge.  Quality  of  steam  96  per  cent.  Thermal  value  of  coal 
14,400  thermal  units  per  pound.  Efficiency  of  boiler  .70.  Find 
the  pounds  of  water  evaporated  per  pound  of  coal  into  steam  of 
the  given  quality. 

Operation : 

Heat  in  the  water  at  boiling  point 361.3 

Heat  in  the  feed  =  140  —  32 108 


Difference   253.3 

Latent  heat  per  pound  =  838.9. 

Take  .96  of  this 805.3 

Heat  required  per  pound  of  moist  steam ,  . .  .    1058.6 

Heat  available  per  pound  of  coal  =  .70  X  14,400  —  10,080. 

Hence  pounds  of  steam  evaporated  =  10,080  ~  1058.6 
—  9-52. 

(3)  Temperature  of  feed  100°.  Steam  pressure  120  pounds, 
gauge.  Evaporation  8  pounds  per  pound  coal.  Assuming  dry 
steam,  what  is  the  evaporation  from  and  at  212°,  and  what  is  the 
factor  of  evaporation? 

Operation : 

Heat  in  the  water  at  boiling  point 322.1 

Heat  in  the  feed  =  100  —  32  = 68.0 


Difference   254.1 


458  PRACTICAL  MARINE  ENGINEERING. 

Latent  heat  per  pound 866.6 


Heat  required  per  pound  of  dry  steam 1 120.7 

Heat  utilized  per  pound  of  coal  =  8  X   1120.7  —  8965.6. 

Evaporation  from  and  at  212°  =  8965.7  —  966  =  9.28. 

Factor  of  evaporation  =  1120.7  -f-  966  =  1.16. 

Evidently  also 

Equivalent  evaporation  —  8  X  1.16  =  9.28. 

(4)  Same  as  in  example  (3)  but  assuming  the  steam  of  95 
per  cent  quality,  what  are  the  results? 

Operation : 

Heat  in   the  water  at  boiling  point 322.1 

Heat  in  the  feed  =  100  —  32  =  68.0 


Difference 254.1 

Latent  heat  per  pound  =  866.6. 

Take  .95  of  this 823.3 


Heat  required  per  pound  of  moist  steam IO774 

Factor  of  evaporation  =  1077.4  -r-  966  =   1.115. 

Equivalent  evaporation  =  8  X  1.11$  =  8.92. 

(5)  Temperature  of  feed  160°.  Steam  pressure  200  pounds, 
gauge.  Quality  of  steam  97  per  cent.  Evaporation  8.8  pounds 
steam  per  pound  coal.  What  is  the  equivalent  evaporation 
from  and  at  212°,  and  what  is  the  factor  of  evaporation? 

Operation : 

Heat  in  the  water  at  boiling  point 361.3 

Heat  in  the  feed  =  160  —  32  =  128.0 


Difference   233.3 

Latent  heat  per  pound  =  838.9. 

Take  .97  of  this 813.7 

Heat  required  per  pound  of  moist  steam 1047.0 

Factor  of  evaporation  =  1047.0  -r-  966  =  1.084. 

Equivalent  evaporation  =  8.8  X  1.084  —  9-54- 

(6)  Compare  the  economy  in  (3)  and  (5). 
Ans.  in  the  ratio  9.28  :  9.54  or  i   :  1.028. 

(7)  Which  is  the  more  economical  of  the  following  cases  : 
(a)  Coal  at  $4.00  per  ton,  9.2  pounds  of  steam  per  pound  of 


SPECIAL    TOPICS   AND   PROBLEMS.  459 

coal ;  quality  of  steam  98  per  cent. ;  steam  pressure  150  pounds, 
gauge;  temperature  of  feed  110°. 

(b)  Coal  at  $3.20  per  ton;  8.0  pounds  of  steam  per  pound 
of  coal ;  quality  of  steam  96  per  cent. ;  steam  pressure  135  pounds, 
gauge  ;  temperature  of  feed  120°. 

By  the  methods  of  the  preceding  examples  we  find  that  the 
equivalent  evaporations  in  the  two  cases  are  as  follows : 

(a)  :  10.46. 

(b)  :  "8.85. 

The  cost  of  steam  in  the  two  cases  will  therefore  be  in  the 
compound  ratio.  (See  Part  II.,  Sec.  6  [2]) : 

(a)    :  (b)    :    :  4.00    :     3.20. 
:    :  8.85    :   10.46. 

or     (a)    :  (b)    :    :  4.00  X  8.85   :  10.46  X  3-2O. 
Whence  (a)   :  (b)   :   :  1.058  :  I 

or  case  (a)  is  nearly  6  per  cent,  more  expensive  than  (b). 

NOTE. — In  solving  the  above  examples  the  heat  in  the  water 
at  boiling  point  has  been  taken  from  the  tables.  Somewhat  more 
quickly  such  problems  may  be  solved  by  taking  the  heat  in  the 
water  at  boiling  point  as  measured  simply  by  the  difference  in 
temperatures,  as  explained  in  Sec.  57  [4]  (i).  The  difference 
is  small  and  is  very  commonly  neglected.  In  the  above  examples, 
however,  we  have  preferred  to  use  the  more  exact  values.  The 
simpler  form  of  solution  will  be  illustrated  by  solving  example 
(5)  in  this  way,  and  the  result  will  serve  to  show  the  nature  of 
the  difference  between  the  two.  We  have  thus : 

Temperature  of  steam 387.7 

Temperature  of  feed 160 

To  raise  one  pound  feed  to  boiling  point 227.7 

Latent  heat  for  one  pound  =  839.9. 

Take  .97  of  this 813.7 


Heat  required  per  pound  moist  steam 1041.4 

Factor  of  evaporation  —  1041.4  -^  q.66  —  1.077. 
Equivalent  evaporation  =  1.078  X  8.8  =  9.49. 

[3]  Evaporation  Per  Pound  of  Combustible. 

In  discussing  further  the  details  of  stenm  boiler  perform- 
ance, it  is  often  desirable  to  make  the  necessary  allowance  for 
the  ash  in  the  coal,  or  for  the  ash  and  moisture,  so  as  to  obtain 


460  PRACTICAL  MARINE  ENGINEERING. 

the  evaporation  per  pound  of  actual  combustible  matter.  To 
this  end  it  is  only  necessary  to  divide  the  evaporation  per  pound 
of  coal  determined  as  above  by  the  fraction  of  the  coal  which 
is  combustible,  or  what  is  the  same  thing,  we  may  increase  the 
result  per  pound  of  coal  in  the  ratio  in  which  the  coal  is  greater 
than  the  combustible.  The  result  will  be  the  evaporation  per 
pound  of  coal  exclusive  of  ash  or  of  ash  and  moisture.  This 
result  may  relate,  of  course,  either  to  the  actual  evaporation 
under  the  given  conditions,  or  to  the  equivalent  from  and  at  212°. 
This  will  be  illustrated  by  the  following  examples : 

(8)  In  example  (5)  Suppose  the  ash  to  be  12  per  cent.,  what 
are  the  actual  and  equivalent  evaporations  per  pound  of  moist 
combustible? 

Ans :  Actual  evaporation  =  8.8  -£-  .88  =  10  Ibs. 

Equivalent  evaporation  =  9.54  -i-  .88  =  10.84  Ibs. 

(9)  Under  the  same  conditions  suppose  the  ash  and  mois- 
ture to  be  15  per  cent.,  what  are  the  evaporations  per  pound  of 
dry  combustible? 

Ans:  Actual  evaporation  =  8.8  -f-  .85  =  10.35. 

Equivalent  evaporation  =  9.54  -r-  .85  =  11.22. 

Sec.  59-  STEAM  ENGINE  ECONOMY. 

[i]  General  Principles. 

In  the  following  discussion  it  will  be  assumed  that  the 
reader  has  a  general  knowledge  of  the  chief  properties  of  steam 
and  of  its  relation  to  the  heat  which  it  contains.  We  will  then 
take  up  in  an  elementary  way  a  discussion  of  the  principles 
governing  its  economical  use  in  a  steam  engine. 

At  the  very  outset  it  must  be  clearly  understood  that  we 
derive  the  work  of  the  engine  from  the  heat  which  the  steam 
contains,  and  not  from  the  steam  in  itself.  The  steam  is  simply 
a  carrier  for  the  heat  and  the  operation  of  the  engine  is  simply 
a  means  for  transforming  into  useful  work  a  fraction  of  the  heat 
which  comes  into  the  engine,  and  then  rejecting  the  remainder 
with  the  steam  which  is  its  carrier.  The  larger  the  fraction  of 
the  heat  which  can  be  transformed  into  useful  work  the  better 
the  efficiency  of  the  engine,  and  the  constant  aim  is  therefore 
to  turn  into  useful  work  the  largest  possible  fraction  of  the  heat 
which  enters  with  the  steam. 

It  may  be  asked,  why  not  turn  all  the  heat  into  work,  and 
so  realize  a  perfect  efficiency?  Unfortunately  a  series  of  natural 


SPECIAL    TOPICS   AND   PROBLEMS.  461 

laws  and  limitations  seems  to  prevent  all  hope  of  realizing  such 
an  ideal,  and  actually  we  must  be  content  with  turning  into  useful 
work  a  comparatively  small  fraction  of  the  total  heat  supplied. 
First  and  foremost  among  the  causes  of  this  reduction  in  effi- 
ciency is  a  principle  or  law  sometimes  known  as  the  second  law 
of  thermodynamics.  This  law  fixes  a  limit  on  the  fraction  of 
heat  which  can  be  transformed  into  useful  work,  such  limit  de- 
pending on  the  extreme  temperatures  between  which  the  sub- 
stance is  worked  in  the  engine.  Thus  if  U  is  the  temperature 
of  the  steam  at  admission  and  t*  that  at  exhaust,  so  that  h  and  t* 
are  the  two  temperatures  between  which  the  steam  is  worked, 
and  (/i  —  fr)  is  the  range,  then  the  law  asserts  that  no  engine, 
no  matter  how  perfect,  can  transform  into  useful  work  a  fraction 
of  the  entering  heat  greater  than  (fr  --  fc)  -f-  (h  +  461).  As 
another  way  of  stating  this  relation,  the  temperature  may  be 
supposed  to  be  measured  from  a  point  461,  or  more  accurately 
460.7  degrees,  below  the  ordinary  zero  of  the  Fah.  scale.  This  is 
called  the  absolute  zero,  and  temperature  measured  from  this 
zero  is  called  absolute  temperature.  The  difference  of  the  tem- 
peratures would  be  the  same  no  matter  whether  measured  from 
the  ordinary  of  absolute  zero.  The  numerator  of  the  above  frac- 
tion is  therefore  the  difference  or  range  of  temperature,  while  the 
denominator  is  the  absolute  temperature  of  the  entering  steam. 
The  fraction  of  heat  converted  into  useful  work  can  therefore 
never  exceed  the  temperature  range  divided  by  the  absolute  tem- 
perature of  the  entering  steam.  Thus  to  illustrate,  suppose  that  h 
=  370  and  ts  =  140.  Then  the  fraction  becomes  (370  —  140)  -4- 
(370  -f-  461  or  230  -i-  831  =  .277  or  slightly  over  one-quarter. 

These  figures  represent  the  limits  for  steam  of  about  160 
pounds  gauge  pressure,  and  it  therefore  appears  that  for  engines 
operating  between  these  limits  this  law  steps  in,  and  at  one 
stroke  reduces  the  ideal  efficiency  from  one  to  about  one-quar- 
ter ;  or  in  other  words  we  are  forced,  due  to  the  operation  of  this 
law,  to  throw  away  about  three-quarters  of  the  total  heat,  and 
at  the  very  best  with  the  most  ideally  perfect  engine  could  only 
transform  into  useful  work  the  remaining  one-quarter. 

Such  then  is  the  very  best  that  could  be  done  by  a  so-called 
ideal  engine.  The  working  substance  in  the  simplest  form  of 
such  an  engine  must  be  carried  through  a  series  of  changes  or 
operations,  four  in  number,  and  specified  as  follows : 

(i)  The  first  operation  must  consist  of  an  expansion  at  con- 


462  PRACTICAL  MARINE  ENGINEERING. 

stant  temperature,  and  all  heat  received  from  the  source  of  sup- 
ply must  be  received  during  this  operation. 

(2)  The   second   operation  must   consist   of   an   expansion 
with  decrease  of  temperature  during  which,  however,  no  heat 
as  such  is  allowed  to  either  enter  or  leave  the  substance. 

(3)  The   third   operation   must   consist   of   a   compression 
during  which  the  temperature  remains  constant  and  all  heat  re- 
moved from  the  body  must  be  removed  during  this  operation. 

(4)  The  fourth  operation  must  consist  of  a  compression  with 
increase  of  temperature,  during  which,  however,  no  heat  as  such 
is  allowed  to  either  enter  or  leave  the  substance,  and  at  the  end 
of  which  the  substance  must  find  itself  in  the  same  condition 
as  at  the  beginning  of  number  (i). 

Work  is  done  by  the  substance  during  operations  (i)  and 
(2)  and  work  must  be  done  on  the  substance  during  (3)  and  (4). 
The  difference  between  the  work  done  by  and  on  the  substance 
will  be  the  net  work  obtained  from  the  heat  in  the  substance, 
and  the  ratio  of  this  to  the  total  heat  supplied  during  number  (i) 
or  the  efficiency  of  the  engine  will  be  exactly  measured  by  the 
difference  between  the  temperatures  of  operations  (i)  and  (3)  di- 
vided by  the  larger  increased  by  461 ;  or  in  symbols  : 

«;  •  'i  —  *. 

efficiency  =   -        —  -  - 

tt  +  461 

This  is  then  the  cycle  and  the  efficiency  of  an  ideal  engine 
in  the  simplest  form.  There  may  be  certain  related  variations  in 
the  operations  (2)  and  (4)  making  a  more  complicated  cycle,  but 
with  the  same  efficiency.  This  ideal  marks,  then,  the  highest 
possible  limit  of  efficiency  for  any  and  all  engines  working  be- 
tween the  given  temperature  limits  ft  and  ft. 

In  the  table  are  shown  the  values  of  this  limiting  efficiency 
for  engines  with  gauge  pressure  as  indicated,  all  condensing  and 
supposed  to  have  a  back  pressure  of  2.8  pounds  absolute,  or  a 
lower  temperature,  ft,  of  140°. 

An  examination  of  this  table  shows  that  with  the  ideal  con- 
ditions which  correspond  to  the  operation  of  this  engine,  the 
fraction  of  heat  utilized  with  modern  boiler  pressures  would 
range  from  25  to  30  per  cent.  These  conditions,  however,  are 
far  from  those  which  actually  exist  in  practice.  Every  one  of 
the  conditions  specified  above  is  violated  in  greater  or  less 
degree,  and  the  result  is  that  with  the  operation  of  the  engine 
under  the  best  conditions  obtainable  in  actual  practice,  the  frac- 


SPECIAL    TOPICS   AND   PROBLEMS.  463 

tion  realized  will  be  only  some  60  to  80  per  cent,  of  the  figures 
for  the  ideal  case  as  given  in  the  table  below.  These  figures,  60 
to  80  per  cent,  in  the  best  practice,  really  measure  the  efficiency 
of  the  engine  so  far  as  the  engineer  is  responsible.  That  is, 
nothing  which  he  can  do  will  serve  to  avoid  the  loss  which  re- 
duces the  limiting  efficiency  down  to  that  for  the  ideal  engine 
as  given  in  the  table  above.  His  efforts  are  therefore  limited 
to  approaching  as  nearly  as  possible  to  the  conditions  of  the 
ideal  engine,  and  the  figures  60  to  80  per  cent,  measure  the  de- 
gree of  approach  which  modern  engineering  practice  has  made 

TABLE. 


Gauge  Pressure 
at  Engine. 

Limiting 
Efficiency 

IOO  

248 

IIO  

253 

1  2O  

259 

130  

264 

140  

269 

ISO  

273 

160  

278 

170  

28l 

180  

285 

190  

289 

200  

292 

210  

295 

22O  

,299 

230  

301 

24O  

304 

25O  

307 

to  this  ideal.  Thus,  for  illustration,  if  the  ideal  engine  could 
transform  25  per  cent,  of  the  heat  into  useful  work,  a  good  actual 
engine  working  between  the  same  temperature  limits  will  be 
able  to  transform  from  15  to  20  per  cent.,  and  similarly  for  other 
conditions. 

To  put  the  matter  a  little  differently,  any  and  all  engines 
fail  to  transform  into  work  all  of  the  heat  supplied  to  them.  In 
the  ideal  engine  as  specified  above,  the  part  not  transformed  but 
rejected  as  heat  is  the  least  possible  for  all  engines  working  be- 
tween the  same  limits  of  temperature  /<  and  h.  In  any  actual 
engine  the  amount  not  transformed  into  work  but  rejected  as 


464  PRACTICAL  MARINE  ENGINEERING. 

heat  is  greater  than  in  the  ideal  case.  Such  additional  amounts 
of  heat  rejected  and  not  transformed  into  work  are  called  wastes 
or  losses.  That  is;  all  differences  between  the  performances  of 
the  ideal  and  actual  engines  are  considered  to  be  due  to  these  so- 
called  wastes  or  losses. 

These  various  wastes  may  be  classified  as  follows  : 

(a)  Radiation  and  Conduction  Waste. 

This  consists  of  heat  which  is  radiated  away  from  the  hot 
surfaces  of  the  cylinder,  or  conducted  away  through  the  columns 
and  bed  plate.  The  heat  thus  escaping  avoids  transformation 
into  work  and  is  therefore  counted  as  a  heat  waste,  or  as  an  ex- 
pense from  which  no  corresponding  return  is  received. 

(b)  Initial  Condensation. 

At  the  instant  the  steam  valve  opens,  the  steam  rushes  into 
the  cylinder  to  find  itself  in  contact  with  surfaces  which  have  but 
recently  been  exposed  to  the  influence  of  the  condenser  or  ex- 
ternal air.  They  are,  therefore,  at  a  temperature  much  lower 
than  the  steam,  and  in  consequence  a  part  of  the  heat  is  absorbed 
and  a  corresponding  part  of  the  steam  is  condensed.  The  heat 
thus  absorbed  by  the  surfaces  of  the  cylinder  and  piston  will  be 
given  up  later  during  the  exhaust  period  of  the  revolution,  and 
thus  communicated  to  the  condenser.  It  thus  appears  that  a 
thin  skin  of  metal  on  the  inside  of  the  cylinder  and  on  the  faces 
of  the  cylinder  head  and  piston  may  be  considered  in  a  sense 
as  a  place  of  hiding  into  which  a  portion  of  the  heat  slips  on  the 
entrance  of  the  steam,  and  from  which  it  escapes  to  the  con- 
denser or  air  without  having  taken  part  in  the  cycle  of  the  en- 
gine, and  hence  without  having  contributed  its  part  to  the  usefu) 
work  done.  The  heat  so  escaping  appears  thus  as  an  expense, 
but  without  any  corresponding  return  in  work,  and  therefore  con- 
stitutes a  heat  waste. 

(c)  Irregularities  of  the  Cycle. 

We  have  specified  above  the  four  fundamental  operations  of 
the  ideal  engine  cycle  in  its  simplest  form.  In  the  actual  engine 
none  of  these  is  realized,  and  the  variations  are  all  such  as  to 
count  against  the  efficiency.  Into  the  details  of  these  points  we 
cannot  here  enter,  and  the  broad  statement  must  suffice  that 
with  but  few  exceptions,  the  variations  from  the  routine  specified 
above  for  the  ideal  engine  will  count  against  the  efficiency  and 
occasion  a  heat  waste  greater  or  smaller  as  the  circumstances 
mav  determine. 


SPECIAL    TOPICS    AND    PROBLEMS.  4^5 

The  Improvement  of  the  Steam  Engine. — From  the  preceding 
section  it  follows  that  there  are  two  fundamental  methods  open 
for  the  improvement  of  the  steam  engine  from  the  standpoint  of 
economy. 

(1)  An  increase  in  the  temperature  range  and  thus  an  in- 
crease in  the  ideal  or  limiting  efficiency. 

(2)  The  saving  of  some  of  the  various  wastes  as  noted 
above. 

The  first  raises  the  ideal  efficiency  and  hence  with  a  given 
proportion  of  wastes  will  raise  the  actual  efficiency  as  well. 
The  second  raises  the  actual  efficiency  by  carrying  it  a  little 
nearer  to  the  ideal. 

The  temperature  range  may  be  increased  in  two  ways, — the 
initial  temperature  can  be  raised,  and<  the  final  temperature  can 
be  lowerd. 

The  continually  advancing  pressures  in  modern  practice 
means  a  constant  rise  in  the  upper  temperature,  a  constant  in- 
crease in  the  ideal  efficiency,  and  with  the  same  proportion  of 
losses,  a  corresponding  rise  in  the  actual  efficiency.  This  is  then 
the  real  significance  of  high  pressures  in  modern  practice  so  far 
as  they  are  related  to  the  question  of  economy. 

Again  by  decreasing  the  back  pressure  from  say  18  pounds 
for  a  non-condensing  engine  to  say  3  pounds  for  a  condensing 
engine,  a  very  considerable  decrease  in  the  final  temperature  is 
obtained,  a  corresponding  increase  in  the  temperature  range,  and 
a  resultant  increase  in  actual  efficiency.  This  is  likewise  the 
real  significance  of  the  influence  of  the  condenser  on  the  econ- 
omy of  the  engine. 

In  general  then,  the  proportion  of  heat  wastes  being  the 
same,  the  economy  will  be  better  as  the  initial  pressure  is  higher, 
and  the  back  pressure  is  lower;  or  in  general,  as  the  range  of 
pressure  and  temperature  worked  through  is  the  greater. 

We  may  turn  next  to  the  problem  of  reducing  the  wastes  of 
the  actual  engine,  as  specified  under  the  three  heads  above. 

The  waste  due  to  radiation  and  conduction  cannot  be  wholly 
avoided,  but  the  former,  which  is  by  far  the  larger  of  the  two, 
may  be  much  reduced  by  suitable  lagging  or  non-conducting 
covering.  With  such  provision  the  loss  under  this  head  is 
usually  very  small  compared  with  the  other  losses  mentioned. 

The  waste  due  to  the  so-called  initial  condensation  is  one 
which  may  be  reduced,  but  not  wholly  avoided.  Before  discuss- 


466  PRACTICAL  MARINE  ENGINEERING. 

ing  the  means  suitable  to  this  end  some  further  explanation  of 
the  nature  of  the  loss  will  be  required. 

As  already  pointed  out,  the  action  of  the  metal  walls  in  pro- 
ducing this  loss  depends  on  their  capacity  when  at  a  lower  tem- 
perature, for  absorbing  heat  from  the  steam  (as  during  admis- 
sion) and  for  giving  it  up  when  at  a  higher  temperature  (as  dur- 
ing exhaust).  The  action  depends,  then,  on  the  range  of  tem- 
perature between  admission  and  exhaust,  and  on  the  particular 
readiness  with  which  the  walls  absorb  and  reject  heat  according 
as  they  are  cooler  or  hotter  than  their  surroundings.  There  are 
therefore  two  distinct  features  to  be  considered — the  range  of 
temperature,  and  the  readiness  with  which  the  iron  absorbs  and 
rejects  heat  under  the  conditions  mentioned. 

Now  it  is  found  that  if  the  expansion  through  the  entire 
temperature  range  is  split  up  into  a  series  of  steps,  each  carried 
out  in  a  cylinder  by  itself,  the  loss  under  consideration  is  less 
than  if  the  entire  expansion  should  take  place  in  one  cylinder. 
Carrying  out  this  principle  we  have,  of  course,  the  multiple  ex- 
pansion engine  with  its  total  range  of  operation  divided  among 
several  cylinders  in  series. 

This,  then,  is  the  real  significance  of  the  multiple  expansion 
(compound,  triple,  quadruple,  etc.)  engine,  so  far  as  its  relation 
to  economy  is  concerned — the  splitting  of  the  total  expansion  or 
of  the  total  temperature  range  into  a  series  of  steps  is,  found  to 
reduce  considerably  one  of  the  wastes,  and  so  raise  the  actual 
efficiency  of  the  engine. 

Next  turning  to  the  other  controlling  feature  of  this  loss, — 
the  readiness  of  absorption  and  emission — it  seems  to  be  the 
case  that  once  the  internal  surfaces  become  wetted  or  covered 
with  a  film  of  moisture,  the  absorption  and  emission  of  heat  into 
and  from  the  metal  proceed  with  much  greater  readiness  than 
when  they  are  dry.  In  other  words  the  passage  of  heat  between 
metal  with  a  moistened  surface  and  moist  steam  is  much  more 
rapid  than  between  the  same  metal  with  a  dry  surface  and  dry  or 
superheated  steam. 

In  the  ordinary  steam  engine  we  have,  therefore,  an  action 
of  the  walls  due  to  the  range  of  temperature  employed,  and  to 
the  natural  capacity  of  cast-iron  or  steel  to  absorb  and  emit 
heat  from  and  to  the  steam.  This  is  further  greatly  aug- 
mented by  the  presence  of  a  more  or  less  complete  film 
or  layer  of  water  over  the  surface,  which  arises  from 


SPECIAL   TOPICS   AND   PROBLEMS.  467 

the     condensation     of     the     first     entering     saturated     steam. 

The  use  of  superheaters,  reheaters  and  jackets  is  found  in  a 
general  way  to  decrease  the  readiness  with  which  heat  ex- 
changes occur  between  the  metal  and  the  steam,  and  thus  to 
decrease  the  amount  of  waste  due  to  their  actions.  Thus  in  an 
engine  using  moderately  superheated  steam  we  should  have  the 
same  general  tendencies  as  noted  above  for  the  operation  with 
saturated  steam,  but  less  augmented  because  of  the  smaller 
amount  of  moisture  formed.  In  an  engine  using  steam  super- 
heated to  such  an  extent  as  to  remain  above  the  point  of  satura- 
tion during  its  entire  passage  through  the  cylinders,  no  moisture 
is  formed  and  the  action  of  the  surfaces  is  limited  to  that  which 
can  take  place  between  their  dry  surfaces  and  the  dry  super- 
heated steam.  The  office  of  superheating  is  then  simply  to  re- 
duce the  readiness  with  which  the  exchange  of  the  heat  between 
the  metal  surfaces  and  the  steam  is  effected.  The  results  show 
that  in  such  case  the  reduction  is  real  and  productive  of  a  con- 
siderable increase  in  economy. 

Regarding  the  use  of  reheaters  it  seems  likely  that  their  bene- 
ficial action  will  be  well  marked  in  proportion  as  they  are  able  to 
superheat  the  steam  passing  through  them,  and  thus  act  as  a 
superheater  in  stages,  each  for  the  cylinder  next  beyond. 

The  beneficial  results  gained  by  the  use  of  steam  jackets  are 
in  large  measure  due  to  action  of  the  same  character.  The 
jacket  containing  steam  at  a  temperature  higher  than  that  in  the 
cylinder  transfers  heat  into  the  inner  surface  of  the  cylinder  walls 
and  thus  tends  to  keep  it  dry  and  to  reduce  the  amount  of  heat 
exchange,  and  hence  the  corresponding  waste.  The  steam 
jacket  acts  also  to  some  extent  to  modify  the  character  of  the 
cycle  as  noted  below,  but  most  of  its  useful  action  may  probably 
be  put  down  to  the  hindering  of  heat  exchanges  between  the 
walls  and  the  steam  in  the  cylinder. 

It  must  not  be  forgotten,  however,  that  whatever  gain  is 
thus  effected  within  the  cylinder  is  obtained  at  the  expense  of 
the  heat  drawn  from  the  jacket,  and  the  whole  operation  is  there- 
fore an  attempt  to  reduce  one  loss  by  introducing  another.  If 
the  latter  is  less  than  the  saving  in  the  cylinder,  the  net  result  will 
be  a  gain  equal  to  their  difference.  If  the  latter  is  the  greater  of 
the  two,  the  net  result  will  be  a  loss,  and  if  they  are  equal  the  net 
result  will  be  no  change  in  the  economy  of  the  engine.  These  re- 
lations account  for  the  varying  experience  with  jackets,  but  it 


468  PRACTICAL  MARINE  ENGINEERING. 

now  seems  well  assured  that  when  properly  fitted  and  operated, 
the  result  will  show  a  gain  of  from  5  to  10  per  cent,  over  similar 
conditions  unjacketed. 

We  come  now  to  the  last  principal  division  of  the  wastes  of 
the  actual  steam  engine, — those  due  to  irregularities  in  the  cycle, 
or  in  other  words  to  variations  from  the  routine  of  operations 
which  would  give  the  efficiency  of  the  ideal  engine  as  discussed 
above.  In  this  respect  but  little  can  be  done  to  improve  matters. 
The  use  of  jackets  and  reheaters  may  possibly  affect  the  routine 
in  such  a  way  as  to  bring  it  somewhat  closer  to  the  ideal  condi- 
tions, but  this  is  by  no  means  certain,  and  the  benefit  due  to 
these  appliances  comes  mostly  from  the  decrease  in  cylinder  con- 
densation as  explained  above. 

There  are  methods,  however,  of  modifying  the  cycle  of 
the  engine  by  the  use  of  a  series  feed  water  heater,  in  such  way 
as  to  bring  it  somewhat  nearer  to  the  ideal  cycle.  Such  a  feed 
heater  for  a  quadruple  expansion  engine  may  consist  of  say  three 
chambers  or  heaters  through  which  the  feed  passes  in  series.  In 
the  first  it  is  heated  by  steam  drawn  from  the  L.P.  receiver.  It 
then  passes  on  to  the  second  chamber,  where  it  is  heated  by 
steam  drawn  from  the  second  I. P.  receiver,  and  then  goes  on  to 
the  third  chamber,  where  it  meets  with  steam  drawn  from  the 
first  I. P.  receiver.  As  the  feed  water  thus  becomes  hotter  and 
hotter  it  meets  with  steam  of  higher  and  higher  temperature 
drawn  from  the  successive  higher  receivers  in  the  engine,  and  it 
is  thus  brought  nearly  to  the  temperature  of  the  water  in  the 
boiler.  The  exhaust  from  pumps  may  also  be  turned  into  the 
first  chamber,  thus  making  it  a  means  of  taking  heat  from  their 
exhaust  and  of  returning  it  with  the  feed  to  the  boiler.  In  some 
cases  also  live  steam  of  full  boiler  pressure  has  been  used  in  a 
last  chamber  to  still  further  raise  the  temperature  of  the  feed. 
Various  modifications  may  be  worked  out  in  the  details  of  the 
operation  of  such  feed  heaters,  but  in  all  cases  their  significance 
lies  in  the  fact  that  the  cycle  of  operations  as  a  whole  may  in  this 
way  be  brought  a  step  nearer  to  the  ideal  cycle  than  would  other- 
wise be  the  case.  All  such  changes,  if  made  in  accordance  with 
the  proper  principles,  may  therefore  result  in  a  saving  of  heat  and 
in  a  gain  in  the  economy  of  the  engine,  and  in  this  fact  lies  the 
chief  significance  of  the  feed-water  heater  as  a  feature  of  modern 
engineering  practice.  See  also  Section  30  with  reference  to  the 
same  subject. 


SPECIAL  TOPICS  AND  PROBLEMS. 


469 


[2]   Relation  of  Expansion  to  Economy. 

The  question  of  the  expansion  of  steam  and  its  influence  on 
engine  economy  has  long  held  an  important  place  as  perhaps  the 
chief  factor  in  engine  economy,  and  it  may  therefore  be  well  to 
refer  to  this  feature  in  somewhat  further  detail.  From  the  stand- 
point of  the  preceding  discussion  of  the  question  we  should  say 
that  the  expansion  of  steam  is  favorable  to  economy  because  it 
brings  the  cycle  of  operations  nearer  to  that  for  the  ideal  engine. 
These  points  may,  however,  be  treated  differently  and  in  a  more 
elementary  manner,  and  we  therefore  proceed  to  discuss  the 
question  by  the  actual  comparison  of  the  two  indicator  diagrams 
given  by  an  engine  working  with  and  without  expansion. 

Consider  the  two  cards  C  D  I  H  and  C  D  E  F  H  of  Fig.  277. 
The  first  is  the  card  that  would  be  given  by  using  the  steam  in 
an  engine  with  stroke  C  D  following  to  the  extreme  end,  and 
then  exhausting  along  D  I  H.  The  second  card  is  such  as  would 


C 


G 

Fig.  277.     The  Expansion  of  Steam. 

>* 

be  given  by  the  same  steam  used  expansively  cut-off  taking 
place  at  D  and  the  stroke  continuing  expansively  to  E.  The 
back  pressure  in  each  case  is  represented  by  the  line  H  F.  The 
area  C  D  I  H  represents  the  work  in  one  case  and  the  area  C  D 
E  F  H  in  the  other,  so  that  the  difference  or  D  E  F  I  represents 
the  gain  by  expansive  working.  In  other  words,  if  we  use  the 
steam  full  pressure  up  to  D  and  then  exhaust  it,  we  throw  away 
an  amount  of  work  measured  by  D  E  F  I  which  might  be  saved 
by  expansive  working.  It  is  likewise  true  that  the  exhaust  open- 
ing at  E  causes  a  loss  of  work  E  J  F  which  might  be  saved  by 
continuing  the  expansion  down  until  the  forward  pressure  falls 
to  the  back  pressure  as  at  J.  It  is  rare,  however,  that  we  can 
afford  cylinders  of  sufficient  size  to  carry  the  expansion  to  sucfi 
a  point,  and,  as  may  be  seen,  the  amount  thus  lost  is  smaller 


470  PRACTICAL  MARINE  ENGINEERING. 

and  smaller  as  the  final  pressure  E  G  is  nearer  the  back  pres- 
sure F  G. 

To  illustrate  the  gain  by  expansive  working  let  us  suppose 
the  initial  pressure  L  C  =  100  pounds,  the  back  pressure  L  H 
=  3  pounds,  and  that  the  cut-off  is  at  a  series  of  points  .1  .2  .3, 
etc.  Then  neglecting  the  effect  due  to  clearance,  the  number  of 
expansions  will  be  as  10,  5,  3.3,  etc.,  and  the  ratio  of  saving 
will  be  as  given  in  the  following  table.  The  numbers  in  the 
column  headed  e  give  values  of  the  ratio  DEFI-i-CDIH, 
or  the  ratio  of  the  amount  saved  by  expansion  to  the  amount 
done  before  expansion  begins. 

Point  of  Cut-off.        Expansion  Ratio.  e. 

.1  10.  2. II 

•2  5-  1-55 

•3  3-30  I.I8 

4  2.50  .91 

.5  2.00  .69 

.6  1.66  .51 

•7  143  -36 

.8  1.25  .23 

.9  i. ii  .11 

.10  i.oo  .00 

It  will  be  understood  that  the  figures  of  the  above  table  refer 
to  indicator  cards  such  as  those  of  the  diagram  in  which  there 
is  no  allowance  for  clearance,  compression,  rounding  off  of  cor- 
ners, etc.  These  conditions  are  of  course  taken  in  order  to 
simplify  the  necessary  computations.  The  nature  of  the  results 
would,  however,  be  the  same  in  the  actual  case,  and  these  figures 
may  therefore  be  taken  as  a  sufficiently  close  indication  for  il- 
lustrative purposes. 

It  thus  appears  that  the  gain  is  proportionately  greater  the 
larger  the  number  of  expansions,  and  for  the  highest  efficiency 
we  should  therefore  carry  the  expansion  to  the  highest  limit. 
Practically  there  are  two  considerations  which  fix  an  early  limit 
to  this  extension  of  the  expansion  range.  The  first  is  the  limit 
of  size.  The  greater  the  number  of  expansions  the  larger  the 
engine  and  hence,  especially  for  marine  engines,  we  can  seldom 
afford  weight  enough  to  give  the  number  of  expansions  which 
other  considerations  might  warrant.  The  second  limitation 
comes  from  the  increase  of  internal  or  cylinder  condensation 


SPECIAL   TOPICS   AND   PROBLEMS.  471 

which  increases  with  the  number  of  expansions  until  finally  the 
resulting  waste  would  off-set  the  gain  due  to  the  increase  in 
ideal  efficiency. 

This  loss  is  decreased  by  the  compounding  of  engines,  so 
called,  or  by  the  splitting  up  of  the  total  expansion  into  a  series 
of  steps  in  separate  cylinders.  Hence  with  multiple  expansion 
engines  we  are  able  to  employ  higher  rates  of  expansion  without 
corresponding  losses  from  cylinder  condensation  than  with  a 
single  cylinder;  and  this,  as  we  have  seen  in  [i],  is  the  real  sig- 
nificance of  the  use  of  multiple  expansion  rather  than  simple 
engines. 

[3]  Economy  of  the  Actual  Engine. 

We  have  already  seen  that  the  highest  possible  efficiency  of 
an  ideal  engine  under  usual  conditions  will  be  found  between  25 
and  30  per  cent.,  while  the  actual  engine  at  the  best  will  realize 
only  some  60  or  70  per  cent,  of  these  figures,  or  an  efficiency  of 
say  15  to  20  per  cent,  in  good  practice.  Now  one  horse  power 
is  33,006  foot-pounds  of  work  per  minute,  and  from  the  value  of 
the  work  equivalent  of  heat  this  is  equal  to  33,000  -r-  778  = 
42.42  heat  units  per  minute.  Hence  one  horse  power  means  the 
transformation  of  42.42  heat  units  per  minute  into  mechanical 
work.  It  follows  that  the  heat  which  must  be  supplied  to  the  en- 
gine in  order  to  provide  for  one  horse  power  will  be  given  by  di- 
viding the  number  42.42  by  the  efficiency  at  which  the  transforma- 
tion is  effected.  But  42.42  -f-  15  =  283.  +  and  42.42  -f-  20  = 
212.  -J-.  Hence,  placing  the  limits  a  little  more  broadly,  it  ap- 
pears that  in  good  practice  we  shall  require  from  say  200  to  300 
heat  units  per  minute  for  each  horse  power  developed  in  the  en- 
gine. This  corresponds  to  a  range  of  12,000  to  18,000  heat  units 
per  hour.  Now  remembering  that  each  pound  of  steam  brings  to 
the  engine  roughly  1,000  heat  units,  it  is  clear  that  this  will  cor- 
respond to  a  range  of  steam  consumption  of  say  12  to  18  pounds 
per  I.  H.  P.  per  hour.  These  figures  may  be  taken  as  covering 
the  range  of  good  practice  from  about  the  best  at  present  attain- 
able to  a  value  only  moderately  fair  for  modern  triple  expan- 
sion engines,  or  good  for  the  usual  type  of  compounds. 

Again  each  pound  of  coal  burned  may  be  expected  to  fur- 
nish under  good  conditions  some  9,000  or  10,000  heat  units  to 
the  water  in  the  boiler,  or  to  transform  some  9  or  10  pounds  of 
water  into  steam.  Hence  the  coal  required  per  I.  H.  P.  per 
hour  will  be  given  by  dividing  the  heat  units  or  the  pounds  of 


472  PRACTICAL  MARINE  ENGINEERING. 

steam  required  by  the  amount  of  either  which  may  be  expected 
from  one  pound  of  coal.  This  will  give  a  coal  consumption  of 
from  about  1.2  to  1.8  pounds  per  I.  H.  P.  per  hour,  which  may 
also  be  considered  as  representing  the  upper  part  of  the  range 
of  good  practice  for  triple  and  quadruple  expansion  engines 
under  from  moderately  good  to  the  best  conditions  at  present 
attainable.  In  a  few  exceptional  cases  by  the  use  of  feed  heaters, 
superheated  steam  and  all  means  favorable  to  economy  the  con- 
sumption has  been  reduced  to  i.o  pound  coal  per  I.  H.  P.  per 
hour. 

For  compound  and  simple  condensing  engines  under  good 
to  moderate  conditions  the  steam  consumption  will  rise  to  from 
20  to  30  pounds  of  steam,  corresponding  roughly  to  from  2  to  3 
pounds  of  coal  with  good  boiler  economy,  and  to  perhaps  2.5  to 
3.5  pounds  with  poor  boiler  economy. 

Farther  along  the  line  will  come  engines  perhaps  non-con- 
densing;  and  of  still  lower  efficiency,  such  for  example  as  electric 
light,  centrifugal  pump,  blower,  winch,  and  steering  engines. 
The  steam  required  for  them  may  rise  to  from  40  to  60  pounds  or 
more  per  I.  H.  P.  per  hour,  corresponding  to  a  coal  consump- 
tion of  from  perhaps  4  to  8  pounds,  according  to  the  boiler 
efficiency. 

Still  lower  in  the  scale  of  economy  we  find  the  ordinary 
direct  acting  pump.  Such  pumps  operate  in  the  steam  cylinder 
with  almost  no  steam  expansion,  and  the  piston  speed  is  very 
low,  thus  giving  full  time  for  the  transfers  of  heat  which  cause 
cylinder  condensation.  Due  to  these  and  other  less  important 
causes  the  steam  consumption  may  rise  to  200  pounds  and  more 
per  I.  H.  P.  per  hour,  while  rarely  can  it  be  brought  as  low  as 
100  pounds.  This  corresponds  to  a  coal  consumption  from  say 
10  to  25  pounds,  depending  somewhat  on  the  efficiency  of  the 
boiler.  In  terms  of  absolute  efficiency  these  figures  correspond 
to  from  about  I  to  3  per  cent.,  the  values  thus  ranging  down- 
ward from  the  15  to  20  per  cent,  given  above  as  the  highest 
values  at  present  attainable. 

Sec.   60.    COAly    CONSUMPTION    AND    RELATED 
PROBLEMS. 

As  we  have  already  seen  in  Sec.  59  the  coal  required  per 
I.  H.  P.  per  hour  in  good  practice  is  usually  found  between  say 
1.5  and  2.0  pounds.  Where  especial  attention  is  given  to  econ- 


SPECIAL   TOPICS  AND   PROBLEMS.  473 

omy  the  figure  may  be  reduced  below  the  lower  value  down  even 
to  i  pound  per  I.  H.  P.  per  hour,  while  by  the  neglect  of  due 
attention,  or  in  cases  where  the  conditions  are  such  that  econ- 
omy must  be  sacrificed,  the  value  may  rise  above  the  higher 
limit. 

Let    :  c  denote  the  pounds  of  coal  per  I.  H.  P.  per  hour. 
H  denote  the  I.  H.  P. 

Then  cH  =  pounds  of  coal  per  hour, 

cH  -i-  2,240  =  tons  of  coal  per  hour, 

,  24  cH         3cH          cH 

and  -  or  -       -  or  -     -   =  tons  of  coal  per  day. 

2240  280          93.3 

As  a  thumb  rule  for  a  quick  estimate,  we  may  remember 
that  at  a  coal  consumption  of  1.86  pounds  per  I.  H.  P.  per  hour 
(a  figure  only  moderately  good),  the  coal  required  per  day  will 
be  20  tons  per  1,000  I.  H.  P. 

The  use  of  the  above  formulae  may  be  illustrated  by  the 
following  examples : 

(i)  With  a  coal  consumption  of  1.78,  how  much  coal  will 
be  required  in  the  bunkers  of  a  ship  making  a  seven-day  trip,  the 
I.  H.  P.  being  2,400  and  a  margin  of  10  per  cent,  being  allowed 
for  emergencies? 

^     *  3x1.78x2400 

Coal  per  day  =  -  -  =  45.75  tons. 

28O 

Coal  for  7  days  =  7  X  45-75  =  320.25,  say 320  tons. 

Margin 32  tons. 


Coal  in  bunkers  =   352  tons. 

(2)  Which  will  require  the  more  coal  per  day,  a  ship  with 
9,800  I.  H.  P.  at  1.82  Ib.  per  I.  H.  P.  per  hour,  or  two  ships  each 
of  4,000  I.  H.  P.  at  2.20  Ib.  per  I.  H.  P.  per  hour? 
For  the  first : 

3X  1.82X9800 


280 
For  the  second : 

3X  2.20x8000 


=  191  tons  per  day. 
=  188.5  tons  per  day. 


280 

Difference  2.5  tons. 

(3)  How  long  time  can  a  vessel  steam  on  213  tons  of  coal 
and  how  far  on  a  speed  of  12  knots,  the  I.  H.  P.  being  3,600  and 
the  coal  consumption  being  1.68? 


474  PRACTICAL  MARINE  ENGINEERING. 

1.68X3600 

Coal  per  hour  =  -  -==2.7  tons. 

2240 

Time  213  -4-  2.7  =  78.9  hours. 
Distance  =  78.9  X  12  =  947  miles. 

(4)  A  vessel's  log  shows  420  tons  of  coal  used  in  a  period  of 
9  days,  16  hours.    The  average  I.  H.  P.  was  2,120.    What  was 
the  coal  consumption  per  I.  H.  P.  per  hour? 

Number  of  hours  —  9  X  24  -\-  16  =  232. 

Amount  used  per  hour  — —  =  4055  Ib. 

«3 

Coal  consumption  =  — — ^5-  =  I.QI  Ib. 

2120 

As  a  further  development  of  the  same  problem  we  may  often 
wish  to  find  the  coal  burned  per  mile,  or  per  ton-mile  of  displace- 
ment, or  per  ton-mile  of  cargo.  These  we  may  illustrate  by  the 
following  examples : 

(5)  Given:  Displacement...    =  9,486  tons. 

I.  H.  P =  12,000 

Speed    =  18  knots. 

Coal    consump- 
tion     =  i  .8  Ib.  per  I.  H.  P.  per  hour. 

Cargo  =  2,000  tons. 

Then: 

Coal  per  hour  =  1.8  X  12,000  =  21,600  Ib. 

Coal  per  mile  =  21,600  -f-  18  =  1,200  Ib. 

Coal  per  ton-mile  of  disp.  =  1,200  -4-  9,486  =  .127  Ib. 

Coal  per  ton-mile  of  cargo  =  1,200  -4-  2,000  =  .6  Ib. 

(6)  If  the  same  ship  were  to  be  driven  at  but  half  the  speed, 
only  about  one-eighth  the  I.  H.  P.  would  be  required,  or  say 
1,500  I.  H.  P.,  while  the  cargo  might  be  increased  to  say  5,000 
tons. 

With  the  same  engine  economy  we  should  then  require : 
Coal  per  hour  1.8  X  1,500  =  2,700  Ib. 
Coal  per  mile  =  2,700  -f-  9  =  300  Ib. 

Coal  per  ton-mile  of  displacement  —  300  -4-  9,486  = 
.316  Ib. 

Coal  per  ton-mile  of  cargo  =  300  -f-  5,000  =  .06  Ib. 

(7)  Again  a  case  similar  to  one  of  the  large  modern  ocean 
freighters : 

Displacement    =    27,000   tons. 
Speed  =  13  knots. 


SPECIAL    TOPICS   AND   PROBLEMS.  475 

I.  H.  P.  =  6,600. 

Cargo  =  15,000  tons. 

Coal  consumption  =1.3  lb.  per  I.  H.  P.  per  hour. 

Then: 

Coal  per  hour  =  1.3  X  6,600  =  8,580  lb. 

Coal  per  mile  =  8,580  -i-  13  =  660  lb. 

Coal  per  ton-mile  of  disp.  =  660  -f-  27,000  =  .0244  lb. 

Coal  per  ton-mile  of  cargo  =  660  -4-  15,000  =  .044  lb. 

At  the  other  extreme  take  a  torpedo-boat  of  the  destroyer 
type  as  follows : 

Displacement  =  310  tons. 

I.  H.  P.  =  6,200. 

Speed  =  31  knots. 

Coal  consumption  =  2.2  lb.  per  I.  H.  P.  per  hour. 

Then : 

Coal  per  hour  =  2.2  X  6,200  =  13,640  lb. 

Coal  per  mile  =  13,640  -f-  31  =  440  lb. 

Coal  per  ton-mile  of  disp.  =  440  -j-  310  =  1.42  lb. 

These  examples  illustrate  the  principle  that  per  ton-mile, 
less  coal  is  burned  as  the  ship  is  larger  and  goes  slower,  while 
more  is  burned  as  she  is  smaller  and  goes  faster.  This  is  the  re- 
sult of  the  two  facts. 

(1)  As  the  ship  increases  in  size  the  power  required  per 
ton  of  displacement  for  a  given  speed  decreases,  and  accordingly 
the  larger1  the  ship  the  less  the  coal  required  per  ton  at  a  given 
speed. 

(2)  For  a  given  ship,  as  the  speed  increases,  the  power  and 
hence  the  coal  required  increase  nearly  as  the  cube  of  the  speed 
ratio,  while  the  time  for  a  mile  or  for  a  given  voyage  is  reduced 
only  in  the  simple  ratio  of  the  speeds.     Thus  to  illustrate :     If 
the  speed  is  increased  10  per  cent.,  or  say  from  10  knots  to  n 
knots,   then   the   power  will   be   increased   nearly  in   the   ratio 
(n  -i-  io)3  =3  (i.i)3  =  1.331,  while  the  time  on  the  mile  or  on  a 
given  voyage  will  be  decreased  in  the  ratio  io  -i-  u.    Hence  the 

coal  will  be  changed  in  the  compound  ratio  —  --—  x  ---  or  1.21 

to  i.  Hence  it  appears  that  in  such  case  the  increase  of  speed  in 
the  ratio  i.i  to  i  will  increase  the  coal  per  mile  or  per  voyage  in 
the  ratio  1.21  to  i.  Or  briefly  an  increase  of  io  per  cent,  in  the 
speed  will  mean  an  increase  of  about  20  per  cent,  in  the  total 
coal  required.  Similarly,  of  course,  a  decrease  of  io  per  cent  in 


476  PRACTICAL  MARINE  ENGINEERING. 

the  speed  would  mean  a  decrease  of  about  20  per  cent,  in  the 
total  coal  required.- 

If  there  were  no  other  principle  involved,  it  would  follow 
that  the  slower  a  given  vessel  goes  the  more  cheaply  could  she 
make  a  given  voyage.  This  would  be  true  if  we  could  consider 
only  the  power  in  the  main  engine,  and  assume  for  it  a  constant 
coal  economy.  This  cannot  be  done,  however,  in  the  case 
of  a  single  ship  going  at  different  speeds,  because  as  the  power 
in  the  main  engines  is  decreased  below  its  normal  amount  the 
coal  required  per  I.  H.  P.  increases  continuously.  Furthermore 
the  power  required  for  the  various  auxiliaries  never  decreases 
in  the  same  ratio  as  the  power  of  the  main  engines,  and  for  cer- 
tain auxiliaries  the  power  is  hardly  affected  by  the  change  in 
the  main  engine.  The  coal  required  for  the  auxiliaries  becomes 
therefore  greater  and  greater  relative  to  that  required  for  the 
main  engine.  Due  to  these  facts  it  follows  that  as  the  speed  is 
decreased  a  point  will  be  reached  below  which  the  saving  in  the 
total  coal  required  per  hour  will  be  more  than  offset  by  the  in- 
crease in  the  time  required,  so  that  for  a  given  voyage  the  total 
coal  expense  will  begin  to  increase  rather  than  decrease.  This 
point  is  known  as  the  "most  economical  speed"  and  is  the  speed 
at  which  a  given  voyage  can  be  made  with  the  least  expenditure 
of  coal.  Its  value  will  depend  largely  on  the  amount  and  char- 
acter of  the  auxiliary  machinery  in  operation,  but  is  often  found 
at  a  speed  somewhat  above  half  the  full  power  speed.  In  the 
mercantile  marine  it  is  rare  that  ships  are  operated  at  speeds 
other  than  those  corresponding  to  normal  full  power  conditions, 
so  that  the  determination  of  a  most  economical  speed  is  not  of 
great  importance  in  such  cases.  In  the  naval  service,  however, 
where  economy  may  be  of  more  importance  than  the  reduction 
of  time  required  for  a  voyage,  ships  are  often  operated  at  or 
about  the  most  economical  speed,  and  its  determination  and  the 
principles  fixing  its  location  are  of  importance  in  such  cases. 

Sec.  61.  THE  I/EVER  SAFETY  VALVE  AND  THE  SAFETY 
VALVE  PROBLEM. 

The  spring  loaded  safety  valve  as  described  in  Sec.  17  [i]  is 
used  almost  exclusively  in  modern  practice.  The  ability  to  solve 
problems  relating  to  the  weighted  arm  safety  valve  (see  also 
the  same  section),  is,  however,  required  of  all  candidates  for 
U.  S.  Engineer's  Licenses,  so  that  it  is  of  importance  to 


SPECIAL  TOPICS  AND  PROBLEMS.  477 

thoroughly  understand  the  method  of  solving  the  various  prob- 
lems which  may  arise  in  this  connection.  These  problems  are 
all  special  cases  of  the  general  problem  in  mechanics  which  has 
to  deal  with  the  equilibrium  of  a  body  under  the  action  of  a 
system  of  forces,  and  for  a  clear  understanding  of  the  matter 
the  principles  discussed  and  explained  in  Part  II.,  Sec  12,  must 
be  kept  well  in  mind. 

The  arrangement  of  a  weighted  arm  safety  valve  is  shown 
in  skeleton  in  Fig.  278.  The  steam  presses  upward  on  the  lower 
face  of  the  valve  V,  and  is  opposed  by  three  forces  tending  to 
keep  the  valve  on  its  seat  as  follows  : 

(1)  The  weight  of  valve  and  spindle  direct. 

(2)  The  weight  of  the  lever  with  center  of  gravity  at  some 
point  N  and  pivoted  at  the  fulcrum  O. 

(3)  The  weight  proper  at  M  acting  with  a  leverage  or  arm 
equal  to  MO. 

Now  just  as  the  valve  is  about  to  open,  these  two  sets  of 


M 

? 

1     t 

^                0 

T 

W 

Fig.  278.    The  Safety  Valve  Problem. 

forces,  the  one  acting  upward  and  the  other  acting  downward, 
will  balance.  It  is  furthermore  a  principle  of  mechanics  that 
when  such  forces  are  just  on  a  balance,  the  product  of  the  forces 
by  their  arms  or  leverages  must  make  the  same  sum  in  each 
direction.  Thus  in  the  present  case  the  up  force  at  S  may  be 
considered  as  tending  to  cause  motion  of  the  lever  about  the 
fulcrum  O,  in  the  direction  of  the  hands  of  a  watch,  while  the 
down  forces  at  B  and  W  tend  to  cause  motion  about  the  same 
fulcrum  in  the  opposite  direction.  We  therefore  measure  the 
arms  from  the  fulcrum  point  O. 

Now  if  A  is  the  area  of  the  valve  in  square  inches  and  />  the 
steam  pressure  in  pounds  per  square  inch  by  the  gauge,  the 
total  steam  load  on  the  valve  will  be  the  product  pA.  This  acts 
directly  upward,  and,  as  noted  above,  is  directly  opposed,  as  far 
as  it  goes,  by  the  weight  of  the  valve  and  spindle.  Denote  this 
weight  by  V.  Then  the  difference  (pA-V)  is  the  actual  or  net 
force  transmitted  from  the  valve  to  the  lever  at  S,  and  tending, 
as  noted  above,  to  turn  the  lever  about  O  from  left  to  right.  Let 


478  PRACTICAL  MARINE  ENGINEERING. 

a  denote  the  arm  for  this  force,  or  the  distance  SO  from  the 
center  of  the  spindle  to  the  center  of  the  fulcrum.  Then  (pA-V)a 
is  the  product  of  force  by  arm  for  the  upward  forces.  Let  us 
save  this  and  turn  next  to  the  remaining  or  downward  forces. 
Let  W  denote  the  amount  of  weight  at  M,  and  /  the  arm  or  dis- 
tance MO  from  the  center  of  gravity  of  the  weight  to  the  iui- 
crum.  Also  let  B  denote  the  weight  of  the  lever,  and  c  the  arm 
or  distance  NO,  from  the  center  of  gravity  of  the  lever  to  the 
fulcrum.  Then  (Wl  +  Be)  is  the  sum  of  the  products  for  the 
downward  forces.  By  condition  these  are  equal  when  the  two 
sets  balance  and  the  valve  may  be  considered  as  on  the  point 
of  opening.  Hence  as  an  equation  we  shall  have  : 

Wl  +  Be  =  (pA-y)a  or 

Wl  +  Bc=  p'Aa-Va. 

From  this  equation  we  can  find  the  value  of  any  one  quanj 
tity  which  we  may  wish,  provided  we  know  all  the  others.  Thus 
suppose  we  know  all  but  W.  Then  we  have  : 

l[7_pAa  -  Va—Bc  (, 

7  .............    V1; 

Similarly  if  we  know  all  but  /  we  have  : 
pAa-  Va  —  Bc 

~W~ 

and  if  we  know  all  but  f(  the  pressure  per  square  inch  at  which 
the  valve  will  open  with  a  given  weight  and  location,  we  have  : 


We  may  readily  express  by  rules  the  operations  represented 
by  these  equations  as  follows  : 

Rule  (i)  To  find  the  weight  knowing  the  other  quantities. 
Multiply  together  the  pressure  per  square  inch,  the  area  of  the 
valve  in  square  inches,  and  the  distance  from  the  center  of  the 
valve  spindle  to  the  center  of  the  fulcrum.  From  this  subtract 
the  product  of  the  weight  of  the  valve  and  spindle  by  the  same 
arm  SO,  and  also  the  product  of  the  weight  of  the  lever  by  its 
arm  NO.  Divide  the  remainder  by  the  weight  arm  MO,  and  the 
quotient  will  be  the  weight  desired. 

Rule  (2)  To  find  the  location  of  the  weight  or  length  of  the 
arm  MO  knowing  the  other  quantities. 

Find  the  same  difference  as  in  rule  (i)  and  divide  by  the 
weight  W  '  .  The  quotient  will  be  the  length  of  the  arm  MO. 


SPECIAL  TOPICS  AND  PROBLEMS.  479 

Rule  (3)  To  find  the  pressure  at  which  a  given  valve  and 
weight  will  lift. 

Multiply  the  weight  W  by  its  arm  MO ;  also  the  weight  of 
the  lever  by  its  arm  NO,  and  the  weight  of  the  valve  and  spindle 
by  its  arm  SO.  Add  these  three  products  and  divide  the  sum  by 
the  product  of  the  area  of  the  valve  times  the  arm  SO.  The 
quotient  will  be  the  pressure  desired. 

Example : 

Let  MO  or  /  =  28  in. 

Let  NO  or  c  =  12  in. 

Let  SO  or  a  =  4  in. 

Let  diameter  of  valve  =  3^  in. 

Then  area  of  valve  or  A  =  9.62  sq.  in. 

Let  weight  of  lever  or  B  =  5^2  lb. 

Let  weight  of  valve  or  V  =  4  lb. 

Let  steam  pressure  or  p  —  80  per  lb.  per  sq.  in. 

Then,  pAa  =  80  X  9.62  X  4  =  3078.4. 

Va  =  4  X  4  =  16. 

Bc=$y2  X  12  =  66. 

Then  3078.4  —  16-66  =  2996.4  and  W  =  2996.4  -f-  28  = 
107  lb.  in  round  numbers. 

Or  if  W  were  known  and  /  required,  we  should  find  the  same 
numerator  2996.4,  and  then  have : 

/  =  2996.4  -7-  107  =  28  inches  in  round  numbers. 
Or  if  p  is  desired  we  should  have  : 

Wl  =  107  X  28 =  2996 

Be  =  $y2  X  12 =       66 

Va  =  4X4 =       16 


Sum 

Aa  =  9.62  X  4  =  38.48- 

We  then  have : 

p  =3078  -r-  38.48  =  80  lb.  in  round  numbers. 

General  Remarks  on  the  Problems. — The  arm  /  is  to  be  meas- 
ured from  the  center  of  gravity  of  the  weight  W  to  the  fulcrum 
or  turning  point  O.  Usually  the  weight  is  of  regular  form,  cir- 
cular or  rectangular  in  elevation,  so  that  its  center  ot  gravity  is 
readily  found.  If  the  lever  turns  about  a  pin,  then  the  arm  / 
must  be  measured  to  the  center  of  the  pin.  If  it  is  provided  with 


48o  PRACTICAL  MARINE  ENGINEERING. 

a  link  and  knife  edge  bearing  as  in  Fig.  78  then  /  is  measured  to 
the  bearing  edge.  If  the  center  of  gravity  of  the  weight  W 
and  the  fulcrum  O  are  not  on  the  same  horizontal  line,  then  the 
arm  /  must  be  measured  as  the  horizontal  distance  between  ver- 
ticals drawn  through  these  points. 

The  center  of  gravity  of  the  lever  arm  must  be  obtained 
practically  either  by  measurement  or  by  balancing  on  an  edge 
in  the  familiar  manner.  If  it  is  practically  a  uniform  straight  bar 
the  method  of  measurement  will  be  quite  accurate  ;  if  it  is  taper- 
ing or  irregular  the  method  by  balancing  may  be  preferred.  In 
any  event,  with  usual  proportions,  as  seen  in  the  example  above, 
the  influence  of  the  lever  is  relatively  small,  so  that  a  slight  error 
in  the  values  relating  to  its  weight  or  center  of  gravity  would  be 
of  much  less  importance  than  a  like  proportional  error  in  the 
weight  W  or  its  arm  /. 

The  area  of  the  valve,  A,  should  be  that,  of  course,  of  the 
lower  face,  or  more  accurately,  of  the  opening  at  the  lower  edge 
of  the  seat. 

The  weights  of  the  various  parts  are  of  course  obtained  by 
weighing.  If  this  is  not  practicable,  a  fair  approximation  may 
be  made  by  computation  based  on  careful  measurement.  In  such 
case  the  volumes  are  found  by  the  most  appropriate  means  ac- 
cording to  the  shape  of  the  figure  (see  Sec.  77)  and  then  by  the 
use  of  the  known  weights  of  the  substances  per  unit  volume, 
(see  p.  30)  the  weights  may  be.  found. 

The  general  U.  S.  regulations  relating  to  safety  valves  will 
be  found  among  the  extracts  from  the  Rules  of  the  U.  S.  Board  of 
Supervising  Inspectors  given  in  Sec.  19. 


Sec.  62.  THE  BOILER  BRACE 

As  we  have  seen  in  Sec.  16  all  flat  surfaces  of  any  consider- 
able size,  in  a  boiler,  require  some  support  in  addition  to  that 
which  can  be  furnished  by  their  own  strength.  In  fact  the  whole 
idea  of  bracing  is  to  subdivide  by  the  braces  a  large  flat  sur- 
face into  a  sufficient  number  of  smaller  surfaces,  each  of  which 
shall  be  self-supporting  between  the  points  where  the  braces  are 
connected  to  the  plate.  The  braces  are  then  designed  so  as  to 
be  able  to  carry  the  entire  load  as  a  whole,  and  the  parts  of  the 
plate  between  the  braces  are  simply  required  to  support,  without 
undue  change  of  form,  the  part  of  the  load  which  comes  upon 
them. 


SPECIAL  TOPICS  AND  PROBLEMS. 


481 


To  illustrate  by  a  diagram  let  Fig.  279  represent  a  part  of  a 
boiler  head  requiring  bracing.  Now  imagine  the  plate  entirely 
cut  out  around  the  dotted  line,  and  then  fitted  in  so  exactly  as  to 
make  a  steam  tight  joint.  The  part  thus  cut  out  is  therefore 
entirely  separated  from  the  remainder  of  the  head,  and  without 
some  especial  support  would  be  blown  out  immediately  when 
steam  was  raised.  Now  suppose  the  braces  to  be  so  designed 
that  they  may  be  safely  depended  on  to  carry  the  entire  load  on 
the  plate,  and  thus  keep  it  securely  in  place  in  the  head.  It 
simply  remains  then  for  the  parts  of  the  plate  between  the  braces 
to  support  themselves  without  losing  their  proper  shape,  and 
the  support  is  thus  made  complete.  In  the  actual  boiler  head,  or 
in  all  cases  where  a  flat  surface  has  to  resist  pressure,  the  design 
of  the  braces  is  worked  out  exactly  along  these  lines,  and  no 


/  Aooooooooo 
/  /  ooooooooo 
I  /oooooooooo 
1  /  oooooooooo 

I  /  OOOOOOOOOO 

l_i_opoooopppo 

0000000 

ooooooo 
ooooooo 
ooooooo 
ooooooo 
ooooooo 

000000000\ 

ooooooooo  \ 
ooooooooooX 
oooooooooo  \ 
oooooooooo  \ 

00000000_QOJ 

Fig.  279.     Boiler  Bracing. 

account  is  taken  of  the  strength  of  the  plate  for  the  general  sup- 
port of  the  load  as  a  whole. 

In  designing  boiler  braces  we  have  to  consider  two  things : 

(1)  The  total  load  to  be  supported  and  number  of  braces, 
or  simply  the  load  upon  one  brace  as  determined  by  their  spac- 
ing and  the  steam  pressure. 

(2)  The  safe  load  per  square  inch  of  section  of  brace. 

The  total  load  depends  on  the  area  to  be  supported  and  on 
the  gauge  pressure.  In  figuring  out  the  area,  as  in  Fig.  279,  it 
is  customary  to  consider  that  a  narrow  strip  of  metal  around  the 
outside  will  be  well  supported  by  the  shell  or  by  the  tubes.  The 
width  of  such  strip  is  usually  taken  as  2  or  3  inches,  though 
there  seems  to  be  no  good  reason  why  it  should  not  be  taken 
as  half  the  spacing  or  pitch  of  the  braces.  This  amounts  to  con- 


482 


PRACTICAL  MARINE  ENGINEERING. 


sidering  the  shell  and  tubes  as  effective  bracing  or  support  lor 
that  part  of  the  plate  near  them,  in  the  same  manner  and  to  the 
same  extent  as  for  the  braces  themselves. 

If  the  area  thus  found  is  multiplied  by  the  gauge  pressure, 
the  total  load  results.  The  spacing  of  the  braces  must  then  be 
taken  in  accordance  with  the  principles  and  rules  given  in  Sec.  19. 
The  total  number  of  braces  is  thus  determined,  and  the  average 
load  per  brace  may  be  found  by  dividing  the  total  load  by  the 
number.  Or  otherwise,  after  the  spacing  is  decided  upon,  the 
load  on  each  brace  may  be  found  by  multiplying  the  area  which 
it  supports  by  the  pressure  per  square  inch.  Thus  in  Fig.  28oa 
the  surface  supported  by  the  brace  is  considered  as  the  dotted 
square,  and  the  spacing  being  the  same  both  ways,  its  area 
equals  the  square  of  the  pitch.  In  some  cases  the  spacing  is  not 
the  same  in  both  directions,  as  in  Fig.  28ob.  In  such  case  the 


Marint  Engineering 


Fig.  280.    Boiler  Bracing. 


supported  area  is  found  by  multiplying  together  the  two  pitches. 
Sometimes,  again,  the  braces  are  irregularly  distributed,  and  the 
area  supported  by  one  brace  may  be  roughly  triangular  or  of 
other  irregular  shape.  In  such  case  the  area  which  the  brace  may 
be  fairly  called  upon  to  support  must  be  taken  by  approxima- 
tion, using1  the  best  judgment  which  can  be  brought  to  bear  on 
the  special  circumstances. 

When  the  braces  are  arranged  in  rows  and  columns  as  in 
Fig.  279,  it  will  usually  be  found  that  due  to  the  necessary  spac- 
ing about  the  edges,  the  average  load  is  slightly  less  than  that 
which  would  correspond  to  an  entire  square  or  rectangle,  and  in 
consequence  it  is  usually  safer  to  take  the  load  as  determined 
directly  by  the  area  supported.  Thus  in  Fig.  28oa,  let  the  side 
of  the  square  be  7  inches :  then  the  supported  area  is  49  square 
inches.  Likewise  in  Fig.  28ob,  let  the  pitch  be  14  inches  in  one 


SPECIAL  TOPICS  AND  PROBLEMS.  483 

direction  and  16  inches  in  the  other:  then  the  supported  area 
equals  14  X  16  or  224  square  inches.  Again  in  Fig.  67,  suppose 
that  three  braces  are  to  be  used  to  support  the  approximately 
triangular  area  on  the  back  tube  sheet.  In  such  case  we  make 
a  fair  allowance  for  the  support  about  the  edges,  sketch  in  the 
area  which  the  braces  may  be  called  on  to  support,  sketch  in  the 
braces  so  as  to  divide  the  area  as  evenly  as  possible,  and  either 
compute  the  area  of  the  whole  triangle  and  divide  by  3,  or  com- 
pute the  smaller  areas  separately. 

Turning  now  to  the  second  chief  question,  the  safe  load  to 
be  allowed  per  square  inch  of  section  of  brace,  we  find  that  the 
U.  S.  Rules  provide  that  iron  braces  shall  not  be  allowed  more 
than  6,000  Ib.  per  square  inch  of  section ;  while  for  steel,  if  in- 
spected according  to  regulation,  the  allowance  may  be  as  fol- 
lows:  From  \y$  in.  diameter  to  2^2  in.  diameter,  not  to  exceed 
8,000  Ib.;  and  above  2^/2  in.  diameter,  not  to  exceed  9,000  Ib., 
each  per  square  inch  of  section.  (See  also  Sec.  19). 

It  must  be  noted  that  in  all  cases  the  diameter  is  measured  at 
the  root  of  the  thread  or  at  the  smallest  section.  For  this  reason 
the  threads  are  usually  raised  so  that  the  diameter  at  the  bottom 
is  not  less  than  that  of  the  body  of  the  brace. 

We  have  thus  discussed  the  determination  of  two  necessary 
items — the  load  which  the  brace  is  to  support,  and  the  safe  load 
per  square  inch  of  section.  It  is  clear  then  that  if  we  divide  the 
latter  into  the  former,  the  quotient  will  be  the  necessary  cross 
sectional  area  of  brace.  Having  found  the  area,  we  find  the 
diameter  by  means  of  a  table  of  diameters  and  areas,  or  by  the 
proper  rule  or  formula  of  mensuration.  See  Part  II.,  Sec.  9  [10]. 

These  various  operations  may  be  expressed  in  the  form  of  a 
rule  as  follows : 

(1)  Find  the  area  to  be  supported  by  one  brace,  and  multiply 
this  by  the  gauge  pressure  per  square  inch.    The  product  will 
be  the  load  to  be  supported  by  the  brace. 

(2)  Take  the  safe  load  per  square  inch  of  section  in  accord- 
ance with  the  rule  above  given. 

(3)  Divide  the  total  load  as  found  in  (i)  by  the  safe  load  as 
taken  in  (2)  and  the  quotient  will  be  the  necessary  area  in 
square  inches. 

(4)  Find  the  corresponding  diameter  either  by  the  help  of  a 
suitable  table  or  by  means  of  the  proper  formula  or  rule  of  men- 
suration. 


484  PRACTICAL  MARINE  ENGINEERING. 

To  illustrate  the  foregoing  a  few  examples  will  be  of  aid. 

(1)  In  Fig.  279,  suppose  the  total  area  to  be  supported  is 
found  by  measurement  to  be  3,784  square  inches,  the   steam 
pressure  being  160  pounds  gauge.    Find  the  total  load. 

Ans.    Load  =  3784  x  160  =  605,440. 

(2)  In  Fig.  28oa,  suppose  the  braces  spaced  14  inches  each 
way,  the  steam  pressure  being  the  same  as  in  (i).     Determine 
the  load  on  one  brace. 

Ans.    Load  =:  14  x  14  x  160  =  31,360. 

(3)  Suppose,  instead,  that  we  wished  to  space  the  braces  14 
inches  one  way  and  16  inches  the  other.    Find  the  load  on  one 
brace. 

Ans.    Load  =  14  x  i6x  160  =  35,840. 

(4)  Suppose  that  we   space   screw   staybolts  6  inches  x  6 
inches.    Find  the  load  on  one  brace. 

Ans.    Load  =6  x6x  160  —  5,760. 

(5)  Suppose  in  (4)  that  the  spacing  were  7x6^.    Find  the 
load. 

Ans.  Load  =  7  x  6l/>  x  160  =  7,280. 

(6)  What  would  be  the  area  and  diameter  of  a  steel  brace  in 
(2),  allowing  8,000  Ib.  per  square  inch  of  section? 

Ans.    Area  =  31,360  -r-  8,000  =  3.92  square  inches. 
Corresponding  diameter  =  2%  inches  nearly. 

(7)  What  would  be  the  area  and  diameter  of  a  steel  brace  in 
(3),  allowing  8,000  Ib.  per  square  inch  of  section? 

Ans.    Area  =  35,840  -i-  8,000  =  4.48  square  inches. 
Corresponding    diameter  =  2  7-16     scant.      Probably    2^ 
inches  would  be  employed. 

(8)  What  would  be  the  area  and  diameter  of  an  iron  stay  in 
(4),  allowing  6,000  Ib.  per  square  inch  of  section? 

Ans.    Area  =  5,760  -h  6,000  =  .96  square  inches. 
Corresponding  diameter  =  i  1-8  inches  nearly. 

(9)  What  would  be  the  area  and  diameter  of  an  iron  stay  in 
(5),  allowing  6,000  Ib.  per  square  inch  of  section? 

Ans.    Area  =  7,280  -~  6,000  =  1.213. 
Corresponding  diameter  =   i*4  inches  nearly. 

(10)  Suppose  that  screw  stay  bolts  are  spaced  7x7  inches, 
the  steam  pressure  being  200  Ib.  gauge.    Find  the  area  and  diam- 
eter of  a  steel  stay,  allowing  8,000  Ib.  per  square  inch  of  section. 

Load  =  7  x  7  x  200  =  9,800  Ib. 

Area  =  9,800  -H  8,000  =  1.225  square  inches. 


SPECIAL    TOPICS   AND   PROBLEMS. 


485 


Corresponding  diameter  =  i  j4  inches  nearly. 

Load  on  Oblique  Braces.  In  case  the  brace  is  not  at  right 
angles  to  the  surface  to  be  supported,  proper  allowance  must  be 
made  for  the  increase  of  load  on  the  brace  due  to  the  angle  of 
obliquity.  This  problem  is  explained  in  Part  II.,  Sec.  12 
[14]  (14)- 

Load  on  Forked.  Ends  of  a  Brace.  The  load  on  the  forked  ends 
of  a  brace,  as  in  Fig.  59,  is  greater  than  one-half  the  load  on  the 
brace,  in  a  ratio  depending  on  the  angle  of  obliquity.  This  prob- 
lem is  explained  in  Part  II.,  Section  12  [14]  (13). 

Sec.  63.  STRENGTH  O       BOILERS. 

In  order  to  examine  the  relation  of  the  strength  of  a  boiler 
shell  to  its  diameter,  thickness  and  the  steam  pressure,  consider 


3  F  H  D 

Uttriiie  t^'iyiiuxrinff 

Fig.  281.     The  Stnt  gth  of  Rollers. 

first  a  hollow  chamber,  as  in  Fig.  281,  with  parallel  sides,  AC  and 
BD,  a  face  AB  perpendicular  to  these  sides,  and  for  the  other  end 
any  other  curved  or  irregular  surface  CD.  Let  this  contain 
steam  under  pressure.  Now  it  is  a  well-known  fact  of  experience 
that  under  such  circumstances  the  chamber  will  remain  in  equi- 
librium, and  it  will  not  move  as  a  whole,  and  in  particular  will 
move  neither  to  the  right  nor  to  the  left.  Hence  the  internal 
force  acting  to  the  right  must  equal  that  to  the  left.  But  the 
force  acting  to  the  right  is  the  total  resultant  of  all  the  forces  act- 
ing on  the  curved  surface  CD,  while  the  force  acting  to  the  left 
is  the  resultant  of  the  parallel  forces  acting  on  the  plane  face  AB. 
Hence  numerically  these  two  resultant*  must  be  equal,  nnd  this 
will  be  the  same,  no  matter  what  the  shape  of  the  surface  on  the 
right,  as,  for  example,  EF  or  GH.  Now  AB  is  called  the  pro- 
jected area  of  any  curved  surface,  such  as  CD,  EF  or  GH,  the 


486  PRACTICAL  MARINE  ENGINEERING. 

direction  of  projection  being  of  course  parallel  to  the  sides  AC 
and  BD.  Hence  we  may  say  that  the  total  resultant  force  in  any 
direction  due  to  the  pressure  of  steam  or  of  any  gas  or  vapor  act- 
ing on  the  curved  surface  will  equal  the  pressure  of  the  projected 
area  of  such  surface,  the  projection  being  taken  in  the  direction 
of  the  resultant  desired.  This  is  a  very  general  and  very  im- 
portant principle  in  mechanics,  and  has  many  applications,  one  of 
which  is  to  the  problem  of  the  strength  of  a  boiler,  as  we  will  pro- 
ceed to  show. 

In  Fig.  282  let  ABCD  denote  a  cross  section  of  a  cylindrical 
boiler  with  steam  pressure  acting  on  the  curved  surface,  as  de- 
noted by  the  arrows.  Suppose  a  plane  of  division  AB,  and  let  us 
consider  what  it  is  which  keeps  the  two  halves  from  separating 
under  the  action  of  the  steam  pressure.  The  surface  ACB  is 


Q        Marine  Engineering 

Fig.  282.     The  Strength  of  Boilers. 

urged  upward  and  the  surface  ADB  is  urged  downward,  while 
they  are  prevented  from  separating  by  the  strength  of  the  ma- 
terial at  A  and  B. 

Now  the  force  tending  to  thus  separate  the  two  parts  is  evi- 
dently measured  by  the  force  urging  ACB  upward  or  ADB  down- 
ward. As  we  have  just  seen,  this  equals  the  force  on  the  pro- 
jected area  which  is  represented  by  AB.  Suppose  the  axial 
length  of  the  section  which  we  are  considering  to  be  one  unit,  or 
one  inch,  and  denote  the  diameter  by  d,  the  radius  by  r  and  the 
thickness  of  the  shell  by  t.  Then  the  area  of  AB  equals  'd.  square 
inches,  and  if  p  is  the  pressure  per  unit  area  the  total  load  on  AB 
is  pd.  But  as  we  have  seen  this  is  numerically  the  same  as  the 


SPECIAL  TOPICS  AND  PROBLEMS.  487 

force  which  urges  ACB  upward  and  ADB  downward,  and 
which  is  opposed  simply  by  the  strength  of  the  material  at  A  arid 
B.  The  cross  sectional  area  on  each  side  will  be  t  x  i  or  /  ;  hence 
the  total  area  of  material  will  be  2t.  Let  5  denote  the  stress  de- 
veloped in  the  material  per  square  inch  of  section.  Then  2/5*  is 
the  total  stress  developed,  and  this  must  equal  the  load  pd* 
Hence  we  have  the  equation  2tS  =  pd  =  2/>r.  (i) 


2/5  tS 

and       p  =  ~~d    =  7  ^3) 

In  these  equations  (3)  gives  the  value  of  the  steam  pressure 
p,  which  would  produce  the  stress  S  in  the  metal  of  thickness  t. 
If,  however,  a  shell,  as  in  Fig.  282,  were  formed  with  riveted 
joints  the  strength  of  the  metal  in  the  joint  would  be  less  than 
that  of  the  plate  itself  in  the  ratio  given  by  the  efficiency  of  the 
joint  as  discussed  in  section  15.  Hence,  if  5  is  to  be  the  safe 
working  stress  in  the  metal  of  the  joint,  and  e  is  the  efficiency, 
the  working  pressure  p  must  be  reduced  in  the  ratio  of  the  effi- 
ciency, or  from  p  to  ep,  in  order  to  keep  the  stress  in  the  joint 
down  to  the  value  S.  Also  if  T  is  the  ultimate  strength  of  the 
metal,  we  do  not  wish  S  to  rise  above  a  certain  fraction  of  T. 
The  number  by  which  we  divide  T  to  find  the  safe  stress  S  is 
called  the  factor  of  safety.  Denote  this  factor  by  f.  Then  in  (3) 
substituting  for  5"  its  value  T  -f-  f  and  allowing  for  the  efficiency 
of  the  joint  we  have  : 

2etT        etT 
P  =  ~jjr  =  -f  (4) 


and         ,  m  (5) 


In  a  similar  manner  let  us  consider  the  strength  of  the  boiler 
to  withstand  rupture  around  the  shell.  In  this  case  the  area  of  the 
head  is  nd2  H-  4  and  the  load  is/nv/2  -~  4.  The  section  of  metal 
carrying  this  load  is  measured  by  the  circumference  multiplied  by 
the  thickness,  or  by  xdt.  Hence  if  5  is  the  stress  developed  per 
unit  area,  the  total  stress  in  the  metal  carrying  the  above  load  is 
ndts.  Equating  the  load  and  the  total  developed  stress  we  have  : 


7T  dtS    = 

4 

4/5  2/5 

or         P  —  ~ 


438  PRACTICAL  MARINE  ENGINEERING. 

Comparing  this  with  (3)  it  is  seen  that  in  the  case  of  the 
shell  without  seam  or  joint  the  pressure  necessary  to  produce 
rupture  around  the  circumference  will  be  just  twice  that  required 
for  rupture  along  the  length  ;  or,  in  other  words,  the  boiler  is 
twice  as  strong  for  rupture  around  the  circumference  as  for  rup- 
ture along  the  length,  and  this  is  an  important  principle  which 
should  be  borne  in  mind  in  dealing  with  questions  relating  to  the 
strength  of  a  cylinder  against  pressure  from  within.  It  also  fol- 
lows that  the  longitudinal  seams  must  be  made  with  the  greatest 
care  and  of  the  highest  efficiency,  while  joints  of  lower  efficiency, 
so  long  as  they  insure  tightness  against  leagage  of  steam,  will 
be  sufficient  for  the  circumferential  seams.  To  take  account  of 
the  factor  of  safety  and  of  the  efficiency  of  the  joint  we  must  in- 
troduce in  (6)  the  factors  /  and'  e,  the  same  as  in  (3).  This 
will  give  :  — 

4etT        2etT 
P  =  ~fd    =  7~^  (?) 


and  ,=  (8) 


For  a  bumped  boiler  head,  as  referred  to  in  section  19,  we 
consider  that  the  head  is  a  part  of  a  sphere,  and  that  all  parts  of 
such  a  surface  are  equally  strong.  Now  for  a  sphere  as  a  whole 
we  have  for  the  total  load  on  a  circumferential  section  the  pres- 
sure p  multiplied  by  the  projected  area  of  the  hemisphere.  But 
the  latter  is  ^2  ~  4,  and  therefore  the  load  is  ^pd^  -f-  4.  The 
total  section  of  metal  is  ndt,  snd  if  5  is  the  stress  developed  per 
unit  area,  then  the  total  stress  is  ndtS.  Hence  we  have  : 

npd* 

=  7T  dtS 

4 

4/J 

or        p  =  £ 

But,  as  seen  above,  this  is  the  same  as  the  value  for  a  cylin- 
drical shell  for  rupture  around  the  circumference.  Hence  we 
have  the  principle  that  a  sphere  has  the  same  strength  in  all  di- 
rections as  a  cylinder  of  equal  diameter  for  rupture  around  the 
circumference.  It  will  be  noted  that  this  relates  simply  to  the 
strength  of  a  sphere  or  part  of  a  sphere  for  pressure  on  the  con- 
cave surface.  For  the  strength  of  a  head  bumped  inward  or  con- 
vex on  the  inside,  there  is  no  method  of  treatment  by  simple 
mechanics. 

For  the  mechanics  involved  in  the  computations  relating  to 


SPECIAL  TOPICS  AND  PROBLEMS.  489 

plain  boiler  bracing  reference  may  be  made  to  section  62  and  to 
Part  II.,  section  12. 

Sec.  64.  JyOSS  BY  BLOWING  OFF. 

In  the  days  of  the  jet  condenser,  and  when  blowing  off  to 
reduce  the  density  of  the  water  in  the  boilers  was  the  usual  prac- 
tice, the  loss  of  heat  occasioned  by  this  operation  was  necessarily 
the  subject  of  consideration,  and  it  became  necessary  to  be  able 
to  compute  this  loss  in  any  given  case.  This  is  most  easily  done 
by  the  simple  application  of  algebraic  methods. 

Let  F  denote  the  pounds  of  feed  water  in  any  given  time, 
and  f  its  density. 

Let  B  denote  the  pounds  of  water  blown  out  in  the  same 
time  and  b  its  density. 

Then  (F — 5)  =  pounds  of  water  evaporated  into  steam  in  the 
same  time.  Likewise  fF  represents  the  amount  of  solid  matter 
brought  into  the  boiler  during  the  giveif  time,  and  bB  represents 
similarly  the  amount  blown  out  in  the  same  time.  Since  the 
density  of  the  water  in  the  boiler  remains  constant  at  b,  the 
amount  of  solid  matter  in  the  water  must  remain  constant,  and 
hence  as  much  must  be  blown  out  as  comes  in  by  the  feed,  or : 
fF  =  bB  (i) 

From  this  we  readily  derive  the  following  relations : 
F        b 
B    =?  ^ 

^B~   =  "/"      (3) 
Now  let  ti  =  temperature  of  feed, 

/a  =  temperature  of  steam, 

H  =  total  heat  in  one  pound  of  steam  at  given 
pressure. 

Then  B  (/»-/»)  =  heat  blown  out,  and  (F-B)  [H-(t^2)]  = 
heat  put  into  the  steam  formed. 

Then  (F  —  B)  (H  +  32)  +  Bt*  —  Fti  =  total  heat. 
Hence  ratio  of  loss  e  is  given  by : 

e  =       X  (',  —  f,} ^ 

By  the  aid  of  the  ratios  above,  this  expression  is  readily  re- 
duced to  the  following  form  : 

^?      __ 


490  PRACTICAL  MARINE  ENGINEERING. 

These  algebraic  operations  may  be  expressed  by  the  fol- 
lowing : 

Rule — (i)  Multiply  the  density  of  the  feed  water  by  the  dif- 
ference between  the  temperatures  of  the  steam  and  of  the  feed. 

(2)  Subtract  the  density  of  the  water  blown  out  from  the 
density  of  the  feed. 

(3)  Add  32  to  the  total  heat  of  i  Ib.  steam. 

(4)  Multiply  together  the  results  in  (2)  and  (3). 

(5)  Multiply  the  density  of  the  feed  by  the  temperature  of 
the  steam. 

(6)  Multiply  the  density  of  the  water  blown  out  by  the  tem- 
perature of  the  feed. 

(7)  Add  the  results  in  (4)  an<I  (5)  and  subtract  from  the  sum 
the  result  in  (6). 

(8)  Divide  the  result  in  (i)  by  that  in  (7)  and  the  quotient 
expressed  in  per  cent  will  give  the  percentge  of  loss. 

Examples :  (i)  Density  of  feed,  f=i. 

Density  maintained  in  boiler,  6  =  2. 
Pressure  of  steam  =  100  pounds,  gauge. 
Temperature  of  feed  ti  =  100°. 
Then  from  tables :    t*  =  337.8, 
andH=  1185. 
337.8  —  100 


Then  loss  ratio,  e  = 


(1185  +  32)  4-337.8  —  2  X  ioo 


or         e= — — —  =  17.5  per  cent. 
1354-8 

We  may  follow  through  the  details  somewhat  differently,  as 
follows : 

The  loss  of  heat  per  pound  of  water  blown  off  equals  (it  —  fr). 
This  equals  337.8 — ioo  or  237.8. 

The  heat  required  per  pound  of  water  evaporated  is 
H — (U — 32).  This  equals  1185 — (100-32)  or  1117.  Now  from  (3) 
it  appears  that  the  amount  evaporated  is  to  the  amount  blown 
out  as  (b — /)  is  to  f  or  as  i  is  to  i.  That  is,  the  amount  evaporated 
equals  the  amount  blown  out.  Hence  for  every  1117  heat  units 
put  into  a  pound  of  steam  237.8  are  lost.  Hence  the  percentage 
loss  on  the  total  heat  employed  is  237.8  -f-  (237.8  +  1117) 

or          e  =  -^'      =  17.5  per  cent,  as  before. 

o  D  i  * 

(2)  Density  of  feed,  f  =  ft. 

Density  maintained  in  boiler,  b  =  ift. 


SPECIAL  TOPICS  AND  PROBLEMS.  4Qi 

Steam  pressure  =  60  pounds  gauge. 
Temperature  of  feed  ft  =  92°. 
Then  from  tables :  ft  =    307.4, 
and  H  =  1175.7. 
Then  percentage  of  loss, 
I  (307-4—  92) 

c       —     ~ 


f  (ii75-7  +  32)  +iX  307-4—  if  X  92 


7X215. 

or  f  -  -—  —  ?-  -  =  -—  —  =  jS.A   per 

6x1207.74-7x307.4  —  13X92          8202 

cent. 

Or  again  by  analysis  :  The  loss  of  heat  per  pound  of  water 
blown  off  equals  (ft  —  ft).  This  equals  307.4  —  92  =  215.4.  The 
heat  required  per  pound  of  water  evaporated  is  H  —  (ft  —  32). 
This  equals  1175.7  —  (92  —  32)  =  1115.7.  Now  from  (3)  it  ap- 
pears that  the  amount  evaporated  is  to  the  amount  blown  out  as 
^4  is  to  %  or  as  6  :  7.  Hence  for  every  6  Ibs.  evaporated  there 
will  be  7  Ibs.  blown  out.  The  corresponding  loss  of  heat  is 
7  X  215.4  =  1507.8.  The  corresponding  amount  of  heat  put  into 
steam  is  6  X  1115.  7  =  6694.2.  The  total  heat  used  is  1507.8  + 
6694.2  =  8202.  The  percentage  of  loss  will  be  then 

1507.8 


8202 


18.4  per  cent,  as  before. 


Sec.  65.   GAIN  BY  FEED  WATER  HEATING. 

As  we  have  seen  in  Sec.  18  a  certain  fraction  of  the  heat  is 
lost  by  way  of  the  funnel.  In  certain  forms  of  feed-water  heat- 
ers, a  part  of  this  loss  is  prevented  by  placing  the  heater  at  the 
base  of  the  funnel  to  absorb  the  heat  of  the  gases  after  they 
have  left  the  tubes.  In  water  tube  boilers  such  arrangements 
are  especially  common,  the  heater  consisting  usually  of  a  con- 
tinuous coil  of  pipe  jointed  up  with  elbows  or  return  bends,  and 
through  which  the  feed- water  passes  before  going  to  the  upper 
drum,  or  point  of  regular  feed  entrance. 

It  thus  becomes  a  question  of  interest  as  to  how  much  sav- 
ing may  be  effected  by  the  feed-water  heater  thus  arranged  to 
utilize  a  part  of  the  heat  in  the  waste  funnel  gases.  This  will 
be  best  illustrated  by  an  example. 

(i)  Temperature  of  feed  110°.  Pressure  of  steam  160  Ib. 
gauge.  Assuming  dry  steam,  what  will  be  the  percentage  gain 
by  heating  the  feed-water  to  170°? 


492  PRACTICAL  MARINE  ENGINEERING. 

From  Table  I  for  the  first  condition  : 
Total  heat  in  i  Ib.  steam  =  ..........................    1  195 

Heat  in  feed-water  =  1  10  —  32  =  ----  ..................       78 

Heat  required  to  form  i  Ib.  steam  =  ..................  1117 

For  the  second  condition  the  heat  units  saved  are  measured 
by  the  difference  in  the  feed-water/'  temperatures,  or  in  this  case 
by  170  —  no  =  60. 

Hence  60  heat  units  have  been  saved  out  of  1117,  and  in 
this  case  the  heat  required  per  pound  of  steam  formed  will  be 
1117  —  60=  1057. 

The  percentage  saving  is  measured  by  60  -f-  1117  =  5.7  per 
cent. 

In  case  the  feed-water  is  heated  by  exhaust  steam  which  is 
not.  sent  to  the  condenser,  and  of  which  the  heat  would  be  other- 
wise wasted,  the  gain  is  found  in  the  same  manner  by  dividing 
the  rise  in  the  temperature  of  the  feed-water  by  the  number  of 
heat  units  needed  to  form  one  pound  of  steam  without  the  heater. 

In  case  the  feed-water  is  heated  by  live  steam  from  certain 
of  the  receivers,  or  by  any  steam  which  might  otherwise  have 
been  used  or  the  heat  of  which  might  have  been  saved,  then  the 
question  of  heater  economy  becomes  much  more  complicated 
and  cannot  be  determined  by  any  process  of  simple  computation. 
It  becomes  simply  a  question  of  where  it  is  most  advantageous  to 
use  the  heat,  whether  in  the  heater  or  elsewhere,  a  question 
which  in  general  can  only  be  answered  by  the  actual  trial.  See 
also  Sec..  30. 

Sec.  66.  'THE  PROPORTIONS  OF  CYI/TNDERS  FOR 
EXPANSION  ENGINES. 


The  total  expansion  of  the  steam  in  the  multiple  expansion 
engine  is  attained  by  expanding  it  in  the  high  pressure  cylinder 
from  the  point  of  cut-off  to  the  end  of  the  stroke,  and  then 
handing  it  over  to  a  series  of  cylinders  of  continually  increasing 
size  until  the  steam  which  first  filled  the  H.  P.  cylinder  to  the 
point  of  cut-off,  finally  fills  the  L.  P.  cylinder,  and  the  expansion 
is  complete.  It  would  seem  at  first  that  the  total  number  of 
expansions  would  be  given  by  dividing  the  volume  of  the  L.  P. 
cylinder  by  that  of  the  H.  P.  up  to  the  point  of  cut-off.  It  is  not 
quite  true,  however,  that  the  volume  of  the  entering  steam  is 
measured  by  the  volume  of  the  H.  P.  up  to  the  point  of  cut-off, 


SPECIAL  TOPICS  AND  PROBLEMS.  493 

nor  that  its  final  volume  is  that  of  the  L.  P.  cylinder.  These 
simple  relations  are  modified  by  the  clearance  in  the  manner 
described  in  Sec.  68.  Due  to  this  effect  the  actual  number  of 
expansions  will  usually  be  from  .5  to  i  less  than  the  apparent 
number  given  by  dividing  the  H.  P.  volume  up  to  the  cut-off  into 
the  L.  P.  volume. 

The  number  of  expansions  suitable  in  any  given  case  will 
vary  with  the  initial  steam  pressure  and  with  the  other  conditions 
to  be  fulfilled. 

With  steam  having  an  initial  pressure  of  150  to  180  pounds 
and  used  in  triple  expansion  engines  the  number  will  usually 
vary  from  say  8  to  12 ;  toward  the  lower  values  as  the  importance 
of  the  development  of  power  per  ton  of  machinery  is  greater, 
and  the  importance  of  coal  economy  is  less,  and  toward  the 
higher  limit  and  perhaps  even  beyond  in  the  reverse  cases.  With 
higher  steam  pressure,  say  from  180  to  220  pounds, and  quadruple 
expansion  engines,  the  number  of  expansions  will  be  commonly 
found  between  10  and  15,  varying  in  one  direction  or  the  other 
according  to  the  same  general  considerations  as  given  above  for 
the  lower  pressures. 

Of  this  total  expansion  range  not  more  than  1.4  to  1.6  is 
usually  obtained  in  the  H.  P.  cylinder  with  the  usual  cut-off 
between  .55  and  .75  of  the  stroke,  and  taking  into  account  the 
effect  of  the  clearance.  This  leaves  the  remainder  to  be  obtained 
from  the  ratio  between  the  volumes  of  the  H.  P.  and  L.  P.  cylin- 
ders, and  assuming  the  same  stroke  this  will  equal  the  ratio  be- 
tween the  areas  of  the  cylinders.  Hence  with  from  8  to  12  total 
expansions  the  ratio  between  the  piston  areas  of  the  L.  P.  and 
H.  P.  will  usually  be  found  say  from  5  to  7,  while  witfi  a  higher 
steam  pressure  and  from  10  to  15  total  expansions  the  ratio  will 
be  from  say  7  to  10. 

We  shall  not  here  enter  into  the  details  of  the  proportions  of 
the  cylinders  of  multiple  expansion  engines,  and  it  will  be  suffi- 
cient to  add  to  the  foregoing  the  following  simple  rules  by 
which  suitable  values  for  the  diameters  of  intermediate  cylinders 
may  be  found  having  given  those  of  the  high  and  low. 

(a)  For  triple  expansion  engines. 

(1)  Take  the  square  root  of  the  H.  P.  diameter. 

(2)  Take  the  square  loot  of  the  L.  P.  diameter. 

(3)  Multiply  together  the  results  of  (i)  and  (2),  and  the 
result  will  give  a  value  for  the  intermediate  diameter. 


494  PRACTICAL  MARINE  ENGINEERING. 

Example  :  Diam.  of  L.  P.  =  50". 

Diam.  of  H.  P.  =  2o".25. 

1/5Q  —  7.07. 
1/2025  =  4.5. 

4-5  X  7-07  =  31-8. 

It  is  usually  considered  better  to  take  the  actual  value 
slightly  under  rather  than  over  the  value  given  by  the  rules,  and 
we  may  therefore  take  31  or  31  J^  as  a  suitable  diameter  for  the 
intermediate  cylinder. 

(b)  For  quadruple  expansion  engines. 

(1)  Take  the  cube  root  of  the  H.  P.  diameter. 

(2)  Take  the  cube  root  of  the  L.  P.  diameter. 

(3)  Square  the  result  found  in  (i). 

(4)  Multiply  together  the  results  found  in  (2)  and  (3)  and 
the  product  will  give  a  value  for  the  diameter  of  the  first  M.  P. 

(5)  Square  the  result  found  in  (2). 

(6)  Multiply  together  the  results  found  in  (i)  and  (5)  and 
the  product  will  give  a  value  for  the  diameter  of  the  second  M.  P. 

Example  :    Diam.  of  H.  P.  =  27. 
Diam.  of  L.  P.  =  80. 

1/27  =  3. 


(3)2  =  9- 

9  X  4-31  =  38.79- 

(4.31)'  =  18.58. 

3  X  18.58  =  5574. 

Here  also  it  is  usually  considered  better  to  take  the  actual 
diameters  slightly  under  rather  than  over  the  values  given  by 
the  rule.  Hence  in  taking  shop  dimensions  we  may  go  under 
rather  thani  over,  and  in  the  present  case  take  say  38  and  55  as 
suitable  values  for  the  diameters  of  the  two  M.  P.  cylinders. 

Sec.  67.  CLEARANCE  AND  ITS  DETERMINATION. 

The  term  clearance  is  used  in  two  senses.  Clearance  proper 
denotes  the  actual  distance  between  the  face  of  the  piston  and 
that  of  the  cylinder  head  when  the  former  is  at  the  end  of  the 
stroke.  That  is,  it  is  the  least  distance  between  the  piston  and 
the  cylinder  head.  In  amount  it  may  vary  from  *4  to  J^  or  J4 
inch,  being  naturally  larger  the  larger  the  engine. 

The  clearance  volume  or  the  percentage  clearance  on  the 
other  hand  is  the  actual  volume  contained  between  the  face  of  the 


SPECIAL  TOPICS  AND  PROBLEMS.  495 

valve  and  the  face  of  the  piston  when  the  latter  is  at  the  end  of 
the  stroke,  or  it  is  such  volume  expressed  as  a  percentage  of  the 
volume  swept  by  the  piston.  The  clearance  should  be  deter- 
mined either  by  measurement  and  computation  from  the  draw- 
ings, or  by  filling  it  with  water  and  measuring  the  amount  re- 
quired. There  are  several  methods  of  procedure.  In  the  first 
place  the  valve  must  be  disconnected  and  blocked  in  mid  position, 
thus  covering  the  ports.  Care  must  also  be  taken  to  provide  by 
the  use  of  putty,  if  necessary,  against  leakage  at  either  the  valve 
or  piston.  Then  place  the  engine  on  the  center  and  by  means 
of  the  indicator  pipe  fill  the  clearance  volume  with  water  by  pail- 
fuls,  weighing  each  pailful  before  pouring  in,  and  the  amount  left 
over  in  the  last  pailful.  Then  knowing  the  weight  of  the  pail,  the 
total  weight  of  water  poured  in  may  be  found.  This  reduced  to 
volume  by  taking  62.5  Ib.  to  the  cubic  foot  will  give  the  clearance 
volume  in  cubic  feet,  and  this  divided  by  the  volume  of  the  piston 
displacement  will  give  the  clearance  percentage.  If  salt  water 
were  used,  64  instead  of  62.5  would  be  used  in  reducing  to 
volume. 

Somewhat  differently  the  mode  of  procedure  may  be  as  fol- 
lows: Place  the  engine  just  one  inch  off  the  center  as  shown  by 
measurements  on  the  guides.  Fill  up>  the  volume  as  before  and 
note  the  weight  required.  Then  move  the  engine  up  to  the  center 
slowly,  catching  the  water  as  it  is  forced  out  and  weighing  as  be- 
fore. The  amount  forced  out  corresponds  to  i  inch  of  piston  dis- 
placement. Subtract  this  amount  from  the  total,  and  the  re- 
mainder represents  the  water  in  the  clearance.  Divide  the  latter 
by  the  amount  representing  one  inch  of  piston  travel,  and  the 
quotient  is  the  number  of  inches  corresponding  to  the  clearance. 
This  divided  by  the  stroke  will  give  the  clearance  percentage. 

As  an  illustration  of  the  first  mode  of  procedure,  suppose 
diameter  =  22  inches,  stroke  =  40  inches,  weight  of  water  to  fill 
clearance  =  85  pounds.  The  volume  of  clearance  =  85  -f-  62.5 
=  1.36  cubic  feet.  The  volume  of  piston  displacement  =  3.1416 
X  ii  X  ii  X  40  -^  1728  =  8.8  cubic  feet,  nearly.  Hence  clear- 
ance percentage  —  1.36  -f-  8.8  =  15.45  per  cent. 

For  the  second  mode  of  procedure  let  the  figures  be  as  fol- 
lows :  Total  weight  of  water  with  engine  i  inch  off  center  =  99 
pounds.  Weight  of  water  forced  out  when  engine  is  brought  to 
center  =  13.5  pounds.  Difference  =  85.5  pounds.  Then  13.5 
pounds  represents  i  inch  of  piston  travel,  and  85.5  pounds  the 


496 


PRACTICAL  MARINE  ENGINEERING. 


whole  clearance.  Hence  85.5  -f-  13.5  =  6.33  inches  =  number 
of  inches  of  piston  travel  giving  a  volume  equal  to  that  in  the 
clearance.  Hence  6.33  -f-  40  inches  =  15.8  per  cent.  =  clearance 
percentage. 

Sec.  68.   THE  EFFECT   OF   CLEARANCE  IN   MODIFYING 

THE    APPARENT    EXPANSION    RATIO    AS 

GIVEN  BY  THE  POINT  OF  CUT-OFF. 

As  we  have  seen  in  Sec.  67,  the  clearance  volume  is  defined 
as  the  volume  or  space  between  the  piston  when  at  the  end  oT 
the  stroke  and  the  face  of  the  valve.  It  comprises  the  "clearance 
proper"  or  space  between  the  piston  when  at  the  end  of  the 
stroke  and  the  cylinder  head,  together  with  the  volume  of  the 
ports  or  passages  leading  from  the  valve  face  to  the  cylinder. 


O  A  Marine  £*<,Vn«Hn0         p 

Fig.  283.     The  Effect  of  Clearance  on  the  Expansion  Ratio. 

The  volume  of  the  clearance  expressed  as  a  fraction  of  the  vol- 
ume swept  by  the  piston  is  usually  known  as  the  clearance  ratio 
or  per  cent.,  and  is  usually  found  in  marine  practice  from  .10  to 
.15,  though  in  some  cases  it  may  rise  as  high  as  .20.  The  steam 
within  this  volume  takes  part,  of  course,  in  all  expansions  and 
compressions  to  which  the  steam  in  the  cylinder  as  a  whole  is 
subjected,  and  its  influence  on  the  apparent  expansion  ratio  must 
therefore  be  considered. 

If  there  were  no  clearance  volume,  then  the  expansion  ratio 
would  be  given  by  dividing  the  total  volume  swept  by  the  piston, 
by  the  volume  up  to  the  point  of  cut-off.  But  this  would  be  the 
same  as  taking  the  reciprocal  of  the  cut-off  ratio.  Thus,  for 
example,  if  the  cut-off  were  at  1/2  stroke  the  expansion  ratio- 
would  be  2 ;  if  at  1/3  stroke,  3;  if,  at  2/3  stroke,  3/2  or  1.5,  etc. 
With  a  clearance  volume,  however,  this  is  modified  as  shown  by 
Fig.  283.  Let  AB  denote  the  volume  swept  by  the  piston  and 
OA  the  clearance  volume  to  the  same  scale,  or  otherwise  let  AB 


SPECIAL    TOPICS   AND    PROBLEMS.  49? 

denote  the  length  of  the  stroke  and  OA  the  clearance  volume  re- 
duced to  stroke  by  dividing  the  volume  by  the  piston  area.  Then 
if  cut-off  is  at  some  point  X  the  actual  volume  of  steam  within 
the  cylinder  and  ready  to  expand  is  denoted  by  OX  rather  than 
by  AX.  Again  at  the  end  of  the  stroke  when  the  piston  reaches 
B,  the  final  volume  of  the  steam  is  OB.  Hence  the  real  expan- 
sion ratio  is  OB/  OX  and  denoting  its  value  by  r  we  have  : 

AB4-OA 
=  AX+O  A 

Now  dividing  both  numerator  and  denominator  of  this  frac- 
tion by  AB  we  have  : 

i  +  OA 
AB 


AX      OA 

AB  +AB 

Now  AX  -f-  AB  is  the  cut-off  ratio,  and  OA  -f-  AB  is  the 
clearance  ratio  or  per  cent.  Denote  the  first  of  these  by  a  and  the 
second  by  c.  Then  we  have  : 

i  +   c 

~-  ^m- 

Examples  : 

(1)  Cut-off  at  */2  stroke,  clearance  10  per  cent. 
Find  the  true  expansion  ratio. 

Operation  :  a  =  3/2  =  .50. 

c  =  10  per  cent.  =  .10. 

i.  oo  +   .10        1.  10 

Hence  r  —  -  -  —  —  ~  =1.83  Ans. 

.50  +   .10  .60 

(2)  Cut-off  at  60  per  cent,  clearance  15  per  cent.    Find  the 
true  expansion  ratio. 

I.  oo  -f    .  i  Z        i.  ic 

Operation:  —    r  —  —  —  =  i  53  Ans. 

.60  +   .15         .75 

Sec.  69.   ENGINE  CONSTANT. 

As  seen  in  Sec.  55  [3]  we  have  for  the  horse  power  formula  : 


33,000  33,ooo 

Now  the  factors  2.LA  -=-  33,000  are  always  the  same  for  any 
one  cylinder,  while  the  other  two  (pN)  will  vary  according  to  the 
conditions.  We  may  therefore  compute  in  advance  the  value  of 
the  factor  (2.LA  -f-  33,000)  and  then  to  find  the  H.P.  we  shall 


498  PRACTICAL  MARINE  ENGINEERING. 

have  simply  to  multiply  these  by  the  other  two,  of  which  one,  p, 
is  found  from  the  cards,  and  the  other,  N,  from  the  counter.  This 
factor  2.LA  -f-  33,000  is  called  the  "engine  constant,"  and  is  often 
thus  computed  as  a  matter  of  convenience,  especially  when  large 
numbers  of  cards  are  to  be  worked  up. 

For  the  power  in  one  end  of  the  cylinder  only  we  have  sim- 
ply to  take  the  factors  LA  -r-  33,000  with  N  and  the  value  of  p 
found  from  the  corresponding  card.  To  allow  for  the  area  of  the 
piston-rod  on  the  lower  side  of  the  piston  in  the  formula  for  the 
full  power,  we  may  use  the  average  area  top  and  bottom  with  the 
average  mean  effective  pressure.  When  there  is  a  difference  in 
the  values  of  the  mean  effective  pressure  top  and  bottom,  this 
will  not  give  quite  the  same  result  as  if  the  two  ends  were  taken 
separately.  The  difference,  however,  is  in  all  ordinary  cases  quite 
unimportant.  See  also  Sec.  55  [3] . 

Example :  Given  a  cylinder  of  diam.  =  36",  stroke  =  42", 
diam.  of  piston-rod  =  5"-  Find  the  constant  neglecting  the  pis- 
ton-rod, and  also  allowing  for  it  as  above  explained. 

Area  of  cylinder  =  1017.9  sq.  in. 

Stroke  =  3.5  feet. 

Constant  =  (2  X  3-5  X  1017.9)  -v-  33,000  =  .2159. 

Next  to  allow  for  the  piston-rod  we  have  for  its  area  19.6 
square  inches.  Taking  this  from  1017.9  we  have  998.3  square 
inches  as  the  area  of  the  lower  side  of  the  piston.  The  mean  of 
the  upper  and  lower  sides  is  then  1008.1.  It  may  be  noted  that  in 
all  such  cases  the  mean  may  be  most  easily  obtained  by  taking 
from  the  upper  area  one-half  the  piston-rod  area,  or  in  this  case, 
by  taking  9,8  from  1017.9,  giving  1008.1  as  above.  We  then 
have: 

Constant  =  (2  X  3-5  X  1008.1)  -=-  33>ooo  =  .2138. 

Sec.  70.    INDICATED  THRUST. 

The  indicated  thrust  in  pounds  may  be  defined  as  the  indi- 
cated power  in  foot  pounds  divided  by  the  product  of  the  pitch  of 
the  propeller  multiplied  by  the  revolutions  per  minute. 

Let:  ;.j 

H  =  I.  H.  P. 

p  =  pitch  of  propeller. 

N  =  revolutions  per  minute. 

T  —  indicated  thrust. 


SPECIAL  TOPICS  AND  PROBLEMS.  499 

>rmula 
T  in  pounds  = 


Then  by  formula : 

33,000  // 


pN 

This  may  be  reduced  to  tons  by  dividing  by  2,240,  and  we 

T-                   33)0oo  H       14.73/7 
have  T  in  tons  =  - ^  —  , — 


Dividing  the  above  value  of  T  in  pounds  by  the  value  of  the 
reduced  mean  effective  pressure  as  given  by  equation  (i)  in  Sec. 
71,  and  we  have  : 

T        33,000  H  iLNA  2  LA 

< 


An  p  33>ooo  p 

It  thus  appears  that  the  ratio  of  the  indicated  thrust  to  the 
reduced  mean  effective  pressure  is  measured  by  twice  the  stroke 
times  the  L.P.  area  divided  by  the  pitch  of  the  propeller.  All 
of  these  are  constants  for  any  given  engine,  and  it  thus  follows 
that  the  ratio  between  the  indicated  thrust  and  the  reduced  mean 
effective  pressure  is  a  constant,  or  in  other  words  that  the  former 
is  in  a  constant  ratio  to  the  latter.  The  indicated  thrust  which  is 
often  considered  as  a  rather  vague  quantity  is  thus  related  to  the 
reduced  mean  effective  pressure,  a  much  better  known  quantity. 

The  indicated  thrust  may  also  be  considered  as  the  actual 
thrust  which  would  be  exerted  if  the  propeller  worked  without 
slip,  and  if  all  the  power  developed  in  the  cylinders  were  used  in 
driving  the  ship  forward  at  the  speed  thus  produced.  Actually 
a  part  of  the  power  is  lost  in  the  friction  of  the  engine  and  in  the 
water  due  to  the  operation  of  the  propeller,  while  the  latter  does 
not  operate  without  slip.  In  consequence  the  actual  thrust  ex- 
erted on  the  thrust  block  is  usually  found  somewhere  about  two- 
thirds  the  indicated  thrust,  computed  as  above. 

Example: 

The  I.  H.  P.  is  1,640,  the  pitch  13  feet,  and  revolutions  148. 
Find  the  indicated  thrust  in  pounds  and  in  tons  : 

„,  .  33,000  X  1.640 

7  in  pounds  =  —  -   -    28,130 

13  X     148 

T  in  tons  =  28,130  -f-  2,240  =  12.56. 

Sec.  71.  REDUCED  MEAN  EFFECTIVE  PRESSURE. 

In  the  multiple  expansion  engine  the  power,  as  we  know,  is 
developed  in  the  various  cylinders,  as  equally  as  the  designer  is 
able  to  bring  about.  The  reduced  mean  effective  pressure  may  be 
defined  as  the  mean  effective  pressure  which,  acting;  in  the  low 


500  PRACTICAL  MARINE  ENGINEERING. 

pressure  cylinder  alone  with  the  same  piston  speed,  would  pro- 

duce the  same  power  as  the  actual  engine  with  its  series  of  cyl- 

inders. 

,    .    Taking  the  usual  formula  for  power,  as  in  Sec.  55  [3]  we 

have  : 


33,000 

and  solving  for  p  we  have 
33,000  H        3^ 

*        2  LrtN       '-  (2  LA/)  A 

Hence  if  the  entire  power  were  to  be  developed  in  the  L.  P. 
cylinder  the  necessary  mean  effective  pressure  would  be  found 
by  the  operations  indicated  by  this  equation,  and  such  would  be 
the  reduced  mean/  effective  pressure,  or  the  mean  effective  pres- 
sure reduced  to  the  L.P.  cylinder.  The  operations  indicated  by 
the  above  equation  may  be  expressed  by  a  rule  as  follows  : 

Rule: 

(1)  Multiply  the  indicated  horse  power  by  33,000. 

(2)  Multiply  twice  the  length  of  the  stroke  in  feet  by  the 
revolutions  (giving  piston  speed)  and  this  by  the  area  of  the  low 
pressure  piston  in  square  inches. 

(3)  Divide  the  result  found  in  (i)  by  that  found  in  (2)  and 
the  quotient  is  the  reduced  mean  effective  pressure  desired. 

To  obtain  a  somewhat  different  expression  for  the  reduced 
mean  effective  pressure  denote  the  areas  of  the  three  pistons 
H.P.,  I.P.  and  L.P.  of  a  triple  expansion  engine,  for  example,  by 
Ai,  As,  A*,  and  the  corresponding  values  of  the  mean  effective 
pressure  in  these  cylinders  by  {H,  p*,  p*.  Then  the  total  power  H 
of  the  formula  (i)  above  may  be  expressed  as  follows  : 

H  _.  (2LN)frA*  +  (*LN)pJ9  +(2LN)fJ3 

33,000 

According  to  (i)  this  value  of  H  is  to  be  multiplied  by  33,000 
and  divided  by  2  LN  times  A*  the  L.P.  piston  area.  This  will 
give  the  following  as  the  value  of  the  reduced  mean  effective 
pressure  : 


According  to  this  formula  the  procedure  for  finding  the  re- 
duced mean  effective  would  be  as  follows  : 

(i)  Divide  the  mean  effective  for  the  H.P.  cylinder  by  the 
ratio  between  the  L.P.  and  H.P.  piston  areas.  This  reduces  tEe 


SPECIAL   TOPICS  AND   PROBLEMS.  501 

H.P.  mean  effective  to  the  L.  P.  piston. 

(2)  Divide  the  mean  effective  for  the  I.  P.  cylinder  by  the 
ratio  between  the1  L.P.  and  I.  P.  piston  areas.    This  reduces  the 
I.P.  mean  effective  to  the  L.P.  piston. 

(3)  Add  together  the  results  found  in  (i)  and  (2)  and  the 
mean  effective  for  the  L.  P.    The  sum  will  be  the  total  mean  ef- 
fective reduced  to  the  L.P.  piston. 

Example: 

Given  for  a  triple  expansion  engine  the  following: 

Diam.  H.P.  cylinder  =  24" 

I.P.  =  38" 

L.P.         "         =  60" 

Length  of  stroke         =  42" 

Revolutions  =  106 

From  sets  of  indicator  cards  suppose  the  mean  effective 
pressures  found  as  follows  : 
For  the  H.P.  /*  =  61.9 
"       "      I.P.    p>  =  30.2 
"      "      L.P.   p*  —  13.8 

Find  the  total  I.  H.  P.  and  the  reduced  mean  effective  pres- 
sure. 

For  the  piston  areas  we  have  from  a  table  of  areas  of 
circles  : 

Al  =      452.4 
Aa  =:   1134.1 
A3  =  2827.4 

Then  finding  the   I   H.   P.  in   each   cylinder  we  have   as 
follows  : 

I.  H.  P.  in  H.  P.  cylinder  =  ........     629.6 

I.  H.  P.  in  I.  P.  cylinder  =  .........     770.2 

I.  H.  P.  in  L.  P.  cylinder  =  .........     877.2 

Total  I.  H.  P.  —  ................   2277.0 

Then  according  to  rule  (i)  for  the  reduced  mean  effective  : 

33,000  x     2277  g2 

1    7  X  106   X     2827.4   = 

According  to   rule  (2)  for  the   same  we   should  have   as 
follows  : 


.  1134.1 

=   6l'9   >'  +    30.*     !     -~-    +    13.8 


or/  =  9.9  +  12.12  +  13.8  =  35.82. 


So*  PRACTICAL  MARINE  ENGINEERING. 

The  results  are  of  course  the  same,  since  the  two  operations 
are  simply  two  methods  of  computing  the  same  quantity.  If  the 
I.H.P.,  revolutions,  length  of  stroke  and  L.P.  piston  area  are 
given,  then  the  first  method  would  be  used.  If  the  mean  effec- 
tives in  the  various  cylinders  are  given,  together  with  the  revo- 
lutions, length  of  stroke,  and  piston  areas,  then  the  second 
method  may  be  used  without  necessarily  finding  the  I.  H.  P. 
at  all. 

Problems : 

(1)  Given  I.  H.  P.  =  5,120. 
L.  P.  area          =  5,612. 
Stroke  48". 
Revolutions       =      112. 

Find  the  reduced  mean  effective  pressure.    Ans.  33.6. 

(2)  From  a  pair  of  H.  P.  indicator  cards  the  mean  effective 
pressure  is  found  to  be  72.6  Ib.    The  diameters  of  the  H.  P.  and 
L.  P.  are  respectively  18  and  48  inches.    Find  the  high  pressure 
mean  effective  reduced  to  the  L.  P.  piston.    Ans.  10.2. 

(3)  In  the  same  engine  as  in  (2)  the  mean  effective  pressure 
for  the  I.  P.  cylinder  is  found  to  be  33.2  Ib.,  and  the  L.  P.  diam. 
is  29  inches.    Find  the  I.  P.  mean  effective  reduced  to  the  L.  P. 
piston.    Ans.  12.1. 

(4)  In  the  same  engine  as  in  (2)  the  L.  P.  mean  effective 
pressure  is  14.1  Ib.    Find  the  entire  reduced  mean  effective  pres- 
sure.   Ans.  36.4. 

Sec.  72.   PRESSURE  ON  MAIN  GUIDES. 

The  load  on  the  crosshead  guides  comes  from  the  load  on 
the  connecting  rod  and  the  obliquity  of  its  line  of  action.  The 
mechanics  of  this  problem  is  considered  in  Part  II.,  Sec.  12  [14] 
(15)  and  the  maximum  value  of  the  load,  which  is  found  when  the 
crank  is  at  right  angles  to  the  center  line,  is  readily  computed 
in  the  manner  there  shown.  It  thus  appears  that  the  maximum 
load  on  the  guide  will  bear  the  same  relation  to  the  load  on  the 
piston  that  the  length  of  crank  does  to  the  connecting  rod.  This 
method  of  computing  the  load  will  be  illustrated  by  an  example. 

(i)  At  about  mid  stroke  given  the  pressure  on  the  top  of 
the  piston  180  Ib.  per  square  inch  and  on  the  bottom  88  Ib.  per 
square  inch.  The  ratio  of  connecting  rod  to  crank  is  4.5  to  i. 
The  area  of  the  piston  is  404  square  inches.  Required  the  maxi- 
mum load  on  the  guide. 


SPECIAL  TOPICS  AND  PROBLEMS.  505 

Net  pressure  on  the  piston  =.  180  —  88  =  92  Ib.  per  square 
inch. 

Net  load  on  the  piston  =  92  X  404  =  37,i68  Ibs. 

Maximum  load  on  guide  —  37,168  H-  4.5  =  8,260  Ibs. 

The  safe  load  on  guides  is  usually  taken  at  from  50  to  70  Ibs. 
per  square  inch.  In  this  case  therefore  taking  60  Ibs.  as  a  safe 
load  per  square  inch  we  should  have : 

Area  needed  =  8,260  ~  60  —  138  square  inches. 

Sec.  73.    FORCE  REQUIRED  TO  MOVE  A  SI,IDE  VAI/VE. 

The  net  load  on  a  slide  valve  is  the  difference  between  the 
steam  loads  on  the  two  sides.  On  the  back  we  have  a  load  clue 
to  the  full  steam  pressure  in  the  steam  chest.  On  the  inside  we 
have  a  more  variable  load  due  partly  to  the  pressure  in  the 
steam  chest  or  cylinder,  and  partly  to  the  exhaust  pressure.  For 
the  low  pressure  cylinder  exhausting  into  the  condenser  the 
exhaust  pressure  is  small  and  is  usually  neglected.  The  area  of 
the  face  subjected  to  pressure  from  the  cylinder  is  also  relatively 
small,  and  for  the  purposes  we  have  now  in  view  is  usually 
omitted.  The  load  on  such  a  valve  is  therefore  taken  simply  as 
the  load  on  the  back,  the  pressure  per  square  inch,  multiplied 
by  the  area  in  square  inches.  Denote  the  pressure  by  p  and  the 
area  by  A.  Then  the  total  load  will  be  pA.  The  resistance  to 
the  motion  of  the  valve  which  must  be  overcome  by  the  valve 
rod  will  be  the  load  pA  multiplied  by  the  coefficient  of  the  fric- 
tion between  the  valve  and  its  seat.  Let  f  denote  this  coefficient, 
and  F  the  force  necessary  to  move  the  valve.  Then  we  have  : 

F=fpA. 

The  values  of  f  will  depend  on  the  condition  of  the  surfaces 
and  on  the  lubrication.  With  well  fitted  and  lubricated  surfaces 
its  value  should  not  exceed  .01  to  .02.  With  dry  surfaces,  es- 
pecially if  they  should  begin  to  abrade,  its  value  may  rise  to  .10 
and  more. 

Example: 

Given  a  low  pressure  slide  valve  with  dimensions  50  inches 
by  60  inches  :  average  excess  of  pressure  in  valve  chest  over 
condenser,  26  Ibs.  Coefficient  of  friction  .02.  Find  load  on  valve 
stem. 

Area  =  A  —  50  X  60  =  3,000  square  inches. 

Load  =  pA  =  26  X  3,000  =  78,000. 

Load  on  valve  stem  =  fpA  =  .02  X  78,000  =  1,560  Ib. 


504  PRACTICAL  MARINE  ENGINEERING. 

In  designing  a  valve  stem  relative  to  such  a  load  it  must 
be  given  a  large  factor  of  safety  in  order  to  provide  for  starting 
the  valve  from  rest  or  where  partly  stuck  to  the  seat,  and  also 
for  extra  stresses  due  to  the  effects  of  inertia. 

For  a  flat  slide  valve  on  a  high  or  intermediate  cylinder,  an 
estimate  must  be  made  of  the  load  on  each  side  and  the  differ- 
ence taken.  Without  serious  error  the  net  pressure  may  be 
taken  as  the  difference  between  the  average  pressure  in  the 
valve  chest  and  in  the  next  following  receiver.  If  then  pi  and 
/>*  are  these  pressures,  (pi  —  p*)  will  be  the  difference,  and 
(pi  —  />*)  A  the  average  load  on  the  valve.  The  remainder  of  the 
operation  is,  of  course,  the  same  as  explained  above  for  the 
low  pressure  valve. 

Sec.  74.  AMOUNT  OF  CONDENSING  WATER  REQUIRED. 

In  Sec.  57  we  have  seen  how  to  find  the  amount  of  heat 
required  to  formv  one  pound  of  steam  of  given  temperature  and 
pressure  from  a  pound  of  feed-water  of  given  temperature.  To 
condense  the  steam  and  reduce  it  back  to  the  condition  of  the 
feed-water  will  require  the  subtraction  of  the  same  amount  of 
heat.  Hence  we  may  find  the  heat  to  be  taken  from  each  pound 
of  steam  in  the  condenser  in  exactly  the  same  manner  as  in  Sec. 
57.  Now  suppose  the  condensing  water  as  it  comes  in  to  have 
a  temperature  of  ft,  and  as  it  is  discharged,  a  temperature  of  t*. 
Then  the  temperature  of  each  pound  will  be  raised  (t* — •  fi)  de- 
grees. This  means  that  it  will  absorb  (t*  —  h)  units  of  heat. 
Then  if  we  divide  this  into  the  number  of  heat  units  which  must 
be  taken  from  each  pound  of  steam,  it  will  give  the  number  of 
pounds  of  condensing  water  which  must  be  provided  to  con- 
dense one  pound  of  steam.  Then  if  we  know  the  amount  of 
steam  to  be  condensed,  the  total  amount  of  condensing  water  is 
readily  found. 

This  may  be  illustrated  by  the  following  example : 

Pressure  of  steam  at  exhaust  =  3.5  pounds,  absolute. 

Corresponding  temperature  =  148°. 

Temperature  of  condensed  water  =  130°. 

Temperature  of  condensing  water  at  entrance  or  h  ==  62°. 

Temperature  of  condensing  water  at  discharge  or  t*  —  98°. 

Then  from  the  steam  tables  we  find  that  1,029  heat  units 
per  pound  must  be  subtracted  in  order  to  condense  the  steam 
and  reduce  it  to  the  condition  of  the  water  in  the  condenser. 


SPECIAL  TOPICS  AND  PROBLEMS.  505 

We  have  also  t*  —  U  =  98  —  62  =  36  =  number  of  heat  units 
absorbed  per  pound  of  condensing  water.  Then  1,029  -f-  36  •= 
28.6  =  number  of  pounds  of  condensing  water  per  pound  of 
steam. 

Let  us  suppose  an  engine  of  2,000  I.  H.  P.  requiring  16  Ibs. 
of  steam  per  I.  H.  P.  per  hour  to  be  condensed  under  these  con- 
ditions. Then  for  the  total  weight  of  water  W  we  have : 

W  =  2,000  X  16  X  28.6  =  915,200  pounds  per  hour. 

And  915,200  -.-  60  =  Ibs.  per  mt.  =  15,253. 

Then  15,253  -f-  64  =  cu.  ft.  sea  water  per  mt.  =  238. 

In  all  ordinary  cases  the  number  of  heat  units  to  be  sub- 
tracted will  not  differ  much  from  1,000,  and  for  a  rough  estimate 
this  number  is  often  taken  without  detailed  computation  from 
the  steam  tables.  Then,  varying  with  the  season  of  the  year 
and  the  locality,  we  may  expect  that  each  pound  of  condensing 
water  will  absorb  from  say  25  to  50  heat  units,  and  hence  that  the 
condensing  water  required  per  pound  of  steam  will  vary  from 
40  to  20. 

Sec/75.  WORK  DONE  BY  PUMPS. 

It  is  sometimes  desired  to  find  the  net  work  done  by  a  pump 
in  handling  a  certain  amount  of  water.  This  may  be  computed 
closely  if  we  know  the  conditions  under  which  the  pump  op- 
erates. It  is  shown  in  mechanics  that  work  may  be  divided  into 
a  volume  factor  and  a  pressure  per  unit  area  factor,  and  this 
form  of  the  expression  for  work  is  usually  most  convenient  for 
use  in  such  cases. 

Let  us  take  first  the  case  of  a  boiler  feed  pump  feeding 
against  a  gauge  pressure  of  160  pounds  and  supplying  16 
pounds  water  per  I.  H.  P.  per  hour  for  2,100  I.  H.  P.  Then  the 
amount  of  water  supplied  will  be  2,100  X  16  =  33,6oo  pounds 
per  hour.  This  equals  33,600  -f-  60  =  560  pounds  per  minute. 
Taking  62.5  pounds  per  cu.  ft.  this  will  occupy  a  volume  of  560 
-:-  62.5  =  8.96  cu.  ft.  This  volume  of  water  is  pushed  into  the 
boiler  against  a  total  pressure  of  160  +  14.7  or  say  175  pounds 
per  square  inch  or  175  X  144  =  25,200  pounds  per  square  foot. 
Hence  we  have:  Work  per  minute  =  25,200  X  8.96  =  225,792 
ft.  Ibs.  Reducing  this  to  horse  power  we  have  :  H.P.  =  225,792  -f- 
33,000  =  6.84.  This  is  the  net  work,  and  assuming  that  there  is 
no  leakage  or  loss  of  steam.  Actually  there  will  be  such  a  loss, 
raising  the  amount  of  water  which  the  pump  must  deliver  by 
from  5  to  10  per  cent  or  more. 


506  PRACTICAL  MARINE  ENGINEERING. 

Now  between  the  steam  cylinder  where  the  total  work  is 
developed  and  the  net  delivered  work  as  above  determined,  there 
is  a  series  of  losses.  These  may  be  classified  as  follows  : 

(1)  Loss  due  to  the  friction  of  the  water  in  the  pipes  and 
to  the  inertia  or  resistance  of  the  valves.    These  items  form  an 
extra  resistance  which  must  be  overcome  in  addition  to  the 
regular  pressure  in  the  boiler. 

(2)  Loss  due  to  the  friction  of  the  pump  itself.     This  like- 
wise forms  an  extra  resistance  as  in  (i). 

(3)  Loss  due  to  the  slip  of  the  pump.    The  pump  plunger 
and  valves  are  rarely  tight  and  a  certain  amount  of  "slippage"  to 
the  water  is  sure  to  occur.    It  results  that  the  volume  displaced 
by  the  pump  plunger  will  be  greater  than  the  volume  delivered 
to  the  feed  pipe,  and  the  work  to  be  done  in  the  water  cylinder 
will  be  increased  in  about  the  same  ratio.    The  slip  is  quite  a 
variable  feature,  being  quite  small  with  good  workmanship  and 
careful  attention,  and  large  under  contrary  conditions.     With 
the  usual  run  of  boiler  feed  pumps,  however,  it  will  rarely  be  less 
than  5  per  cent.,  and  with  lack  of  care  may  readily  rise  to  from 
10  to  20  per  cent. 

The  sum  of  losses  (i)  and  (2)  will  be  found  usually  between 
15  and  20  per  cent.,  and  hence  the  sum  of  the  total  losses  may 
be  expected  to  vary  between  perhaps  20  or  25  and  40  per  cent. 

In  the  present  case,  for  illustration,  assume  the  loss  by  leak- 
age of  steam  at  joints,  etc.,  as.  6  per  cent.  Then  the  water  ac- 
tually delivered  to  the  boiler  will  require  a  net  work  of  6.84  -'- 
.94  =  7.28.  Assume  the  total  losses  between  steam  cylinder  and 
feed  pipes  to  be  33  per  cent.  Then  the  I.  H.  P.  in  the  steam  end 
will  be  7.28  -f-  .67  =  10.87,  and  we  should  therefore  expect  that 
under  moderate  to  fair  conditions  such  a  pump  would  require 
from  10  to  ii  I.  H.  P.  With  the  pump  plunger  and  valves  leak- 
ing badly,  stiff  working  parts  and  generally  poor  conditions,  the 
amount  will,  of  course,  rise  far  above  these  figures.  The  full 
capacity  of  the  feed  pump  would  also  be,  of  course,  consider- 
ably above  these  values.  We  are  here  simply  concerned  with 
an  estimate  of  the  power  actually  required  and  the  net  power 
delivered  under  a  given  set  of  conditions. 

Again  consider  the  case  of  a  centrifugal  pump  for  the 
same  engine  handling  we  will  say  30  pounds  condensing  water 
per  pound  of  steam  condensed.  Then  the  total  amount  of  water 
handled  per  hour  will  be  2,100  X  16  X  30  =  1,008,000  pounds. 


SPECIAL  TOPICS  AND  PROBLEMS.  507 

In  this  case  the  resistance  to  be  overcome  is  due  chiefly  to 
forcing  the  water  through  the  condenser  tubes.  In  some  cases 
also  the  discharge  outlet  is  slightly  above  the  surface  of  the 
water  and  this  additional  lift  increases  the  work  to  be  done. 

The  most  convenient  method  of  computation  in  this  case  is 
to  estimate  the  total  head  equivalent  to  the  resistance  occasioned 
by  the  condenser  tubes,  and  the  lift  of  the  water  above  the  sur- 
face. This  will  be  the  total  height  of  water  which  would  pro- 
duce the  same  pressure  as  must  be  overcome  by  the  pump  at 
the  tips  of  the  vanes.  In  usual  cases  we  may  assume  the  head 
corresponding  to  the  resistance  in  the  condenser  tubes  at  from 
4  to  5  feet.  If  the  water  is  discharged  at  or  below  the  water 
level  this  will  then  be  the  total  head  against  which  the  pump 
works.  In  case,  however,  the  pump  draws  from  the  bilge  as 
when  used  for  freeing  the  ship  of  water,  then  the  total  head  will 
be  the  total  lift  plus  the  head  due  to  the  condenser  tubes,  and  its 
value  may  rise  in  such  cases  to  20  feet  and  more. 

In  such  cases  the  work  done  is  the  product  of  the  weight  of 
water  handled  as  the  force  or  resistance  factor,  multiplied  by  the 
head  as  the  distance  factor. 

In  the  present  case,  assuming  a  total  head  of  6  feet  we  have  : 
Work  per  mt.  =  16,800  X  6  =  100,800  ft.  Ibs. 

or  H.  P.  =  100,800  -f-  33,000  =  3.05. 

The  efficiency  of  such  pumps  is  usually  found  between  .30 
and  .50.  That  is,  between  50  and  70  per  cent  of  the  power  de- 
veloped in  the  steam  engine  operating  the  pumps  is  lost,  chiefly 
in  the  slip  of  the  pump.  Hence  under  fair  conditions  we  may 
assume  that  'this  3.05  H.  P.  will  be  about  40  per  cent,  of 
the  I.  H.  P.  of  the  engine.  Hence  the  latter  will  be  greater  than 
3.05  in  the  ratio  of  100  to  40  or  2^2  times.  Hence  we  have  : 

I.  H.  P.  required  =  about  2*/2  X  3.05  =  about  7.5. 

These  examples  will  serve  to  show  the  methods  to  be  used 
in  working  such  problems,  and  if  the  principles  involved  are  kept 
clearly  in  view  they  may  be  similarly  applied  to  the  solution  of 
many  problems  likely  to  present  themselves  in  engineering  work. 

Sec.  76.  DISCHARGE  OF  STEAM  THROUGH  AN  ORIFICE. 

It  may  be  sometimes  convenient  to  be  able  to  compute  ap- 
proximately the  amount  of  steam  which  will  escape  into  the 
atmosphere  from  a  chamber  under  a  given  pressure  through  an 
aperture  of  given  area. 


5ofc  PRACTICAL  MARINE  ENGINEERING. 

Let  p  be  the  pressure,  supposed  to  be  not  less  than  25  Ibs., 
absolute.  Let  A  =  area  of  aperture  in  square  inches,  and  W  = 
weight  discharged  in  pounds  per  second.  Then  Napier's  rule 
for  the  approximate  value  of  W  is  as  follows : 

w~& 

70 
Thus  given  A  =  .5  sq.  in.  and  p  =  140  we  have  : 

W  =    I4°  X   '    =  i  lb.  per  second. 
7°   X    2 

Take  the  following  problem :  What  weight  of  steam  would 
be  discharged  per  hour  through  a  small  hole  or  crack  of  area 
.005  sq.  in.  under  a  pressure  of  200  pounds  per  sq.  in.? 

Using  the  formula  we  have : 

TJ_        200  x  -005  x  3600  -  , 

W  =  -  -  -  51.4  pounds  per  hour. 

7° 
We  may  thus  realize  the  importance  of  small  leaks. 

Sec.  77.    COMPUTING    WEIGHTS    OF    PARTS    OP 
MACHINERY. 

The  determination  of  the  weights  of  various  parts  of  marine 
engines  and  boilers  is  often  necessary  as  a  part  of  an  estimate 
of  costs  for  repairs  or  for  other  purposes.  Such  determinations 
are  usually  made  by  numerical  computation,  and  consist  in  find- 
ing first  the  volume  of  the  piece  in  question,  and  then  its  weight 
by  the  use  of  factors  such  as  those  given  in  the  Table  on  p.  30. 
The  chief  part  of  the  computation  is  therefore  mensuration,  the 
principles  of  which  are  given  in  Part  II.,  Sec.  9.  We  will  here 
add  some  general  suggestions  regarding  the  application  of  these 
rules,  with  some  additional  methods  which  may  be  used  in 
special  cases. 

[i]  Units  to  be  Used. 

The  dimensions  will  usually  be  taken  either  from  a  drawing 
or  directly  from  the  piece  in  question.  It  may  be  recommended 
as  a  general  rule  to  reduce  all  dimensions  to  inches  as  the  unit 
rather  than  feet  or  feet  and  inches,  the  latter  requiring  the  use 
of  duo-decimal  notation  and  methods  as  explained  in  Part  II., 
Sec.  4  [5].  Where  the  pieces  are  small  and  fractions  of  an  inch 
are  to  be  dealt  with,  it  will  usually  be  most  convenient  to  re- 
duce them  to  decimal  form  rather  than  to  express  them  as  com- 
mon fractions.  In  brief  the  inch  as  the  unit  and  numbers  ex- 
pressed decimally  are  recommended  as  a  general  rule  in  such 


SPECIAL    TOPICS   AND   PROBLEMS.  509 

computations.  The  factors  for  reducing  cubic  inches  to  pounds 
are  then  used  as  given  in  the  Table  on  p.  30,  and  the  weight  is 
readily  found. 

[2]  Approximations  and  Short  Cuts. 

In  computations  of  this  character  absolute  accuracy  does 
not  exist.  In  fact  with  no  physical  measurement  can  absolute 
accuracy  be  attained.  In  practical  life  we  wish  simply  an  ap- 
proximation, a  value  sufficiently  near  for  the  purposes  in  view; 
a  value  so  near  that  the  error  is  not  of  commercial  or  financial 
importance.  All  engineering  measurements  and  computations 
recognize  this  principle,  and  of  the  acquirements  which  may 
come  to  the  engineer  with  experience,  none  is  of  greater  value 
than  that  which  enables  him  to  know  where  to  stop  his  compu- 
tations, how  far  to  carry  his  measurements  and  approximations, 
what  error  will  be  of  importance,  and  what  insignificant.  Thus 
if  we  are  to  measure  the  dimensions  of  a  coal  bunker  in  order 
to  compute  its  volume,  it  is  evidently  absurd  to  note  the  figures 
to  the  fraction  of  an  inch.  We  can  be  by  no  means  sure  that 
the  length,  for  example,  is  uniform  within  any  such  limit,  and 
the  difference  due  to  a  variation  of  ^4  °r  Y^  inch  either  way  will 
be  insignificant  for  the  purpose  in  view.  On  the  other  hand,  if 
we  are  to  measure  a  journal  in  order  to  make  a  new  one  which 
shall  fit  in  the  same  bearing,  the  admissible  error  is  only  a  few 
thousandths  of  an  inch,  and  the  utmost  attainable  accuracy  will 
be  in  order.  So  likewise  if  we  are  finding  the  weight  of  a  sheet 
of  boiler  plate .  an  error  of  l/%  inch  in  the  length  or  breadth 
will  introduce  no  significant  error  in  the  final  result,  while  such 
an  error  in  the  thickness  would  cause  a  most  serious  error  in  the 
result.  The  former  would  make  a  difference  of  perhaps  one 
part  in  1,000  or  so,  while  the  latter  might  cause  an  error  of  one 
part  in  8  or  10. 

Another  point  which  may  also  be  remembered  is  that  a  large 
relative  or  percentage  error  is  more  permissible  in  some  small 
part  of  the  whole  than  in  a  large  part.  Thus  in  a  boiler  an  error  of 
10  per  cent  in  the  weight  of  the  tubes  may  be  of  less  importance 
than  one  of  i  per  cent  in  the  weight  of  the  shell  and  heads,  while 
an  error  of  50  per  cent  in  the  high  pressure  cylinder  cover,  for 
example,  might  make  less  difference  than  one  of  10  per  cent  in 
the  low  pressure  cover.  Of  course  there  should  be  no  excuse  for 
making  any  50  or  10  per  cent  errors,  but  the  principle  may  be 


5ro  PRACTICAL  MARINE  ENGINEERING. 

borne  in  mind  as  a  legitimate  means  of  saving  time  when  a 
roughly  approximate  value  must  be  determined. 

The  most  common  approximations  are  those  which  make 
the  computation  of  volume  simpler  by  substituting  for  the  actual 
body  some  other  of  simpler  form,  and  with  such  dimensions  as 


Fig.  284.    Approximate  Area  of  Segment  of  Circle. 


Marine  Enyintering 

Fig.  285.     Approximate  Area  of  Boiler  Plate. 

to  be  of  equal  volume  so  far  as  judgment  may  be  able  to  deter- 
mine. Such  substitutions  are  often  employed,  but  they  must  be 
used  with  judgment  and  care  in  order  that  the  possible  error  in- 
troduced may  not  be  larger  than  permissible.  No  general  rules 


SPECIAL  TOPICS  AND  PROBLEMS.          5" 

can  be  given  for  such  approximations,  but  the  most  common 
consist  in  substituting  a  rectangle  or  triangle  or  sometimes  a  cir- 
cle, for  a  more  irregular  area ;  or  a  cylinder  or  regular  prism  or 
plate  for  some  irregular  volume. 

Thus  in  Fig.  284,  if  we  wish  to  find  quickly  an  approximate 
value  of  the  segment  of  the  circle  ABC,  we  may  sketch  in  a  tri- 
angle ADC,  so  taking  the  sides  that  the  area  left  out  shall  be 
judged  equal  to  that  taken  in,  and  hence  the  area  of  the  triangle 
may  be  taken  as  an  approximation  to  that  of  the  segment.  This 
area  is  then  readily  found  by  the  usual  rule  for  a  triangle. 

Again,  in  computing  the  area  of  a  front  boiler  tube  sheet,  as 
shown  in  Fig.  285,  we  may  for  a  first  approximation  substitute 
by  judgment  for  the  actual  contour  a  rectangle  ABCD,  and  thus 
quickly  obtain  a  value  which  may  be  sufficiently  close  for  the 
purpose  in  hand. 

Again  we  may  often  add  by  judgment  something  to  one  of 
the  dimensions  of  a  piece  in  order  to  provide  for  additional  or 
irregular  parts  which  would  not  be  included  in  the  regular  geo- 
metrical figures  dealt  with.  Thus  in  finding  quickly  the  approxi- 
mate weight  of  a  cylinder  casting,  provision  may  be  made  for 
the  flanges  by  adding  by  judgment  an  appropriate  amoilnt  to  the 
length  of  the  casting;  or  similarly  for  a  piece  of  shafting  with 
flanged  couplings  at  the  ends. 

It  is  often  necessary  to  divide  a  more  or  less  complicated  piece 
into  several  parts,  each  of  which  may  be  of  some  relatively  sim- 
ple form.  In  some  cases  the  volume  of  one  simple  form  may 
be  subtracted  from  that  of  another,  thus  giving  as  the  remainder 
the  volume  of  a  more  or  less  irregular  form.  Thus,  to  find  the 
volume  of  a  pair  of  brasses  with  square  backs  and  sides,  we  may 
find  the  volume  from  the  outside  dimensions  as  though  the  block 
were  solid,  and  then  the  volume  of  the  cylindrical  hole,  and  take 
the  one  from  the  other. 

Many  such  little  devices  will  suggest  themselves  in  connec- 
tion with  the  details  of  the  work;  but  it  will  be  unnecessary  to 
here  enter  further  into  the  subject. 

In  connection  with  the  rule  of  Pappus,  Part  II.,  Sec.  9  [30], 
we  may  note  the  following  method  of  applying  it  to  the  deter- 
mination of  the  weight  of  such  forms  as  a  piston,  cylinder  head, 
etc.  The  operations  are  as  follows  : 

(1)  The  cross  sectional  drawing  is  supposed  to  be  at  hand. 

(2)  A  copy  of  the  half  cross  section,  as  shown  for  a  piston 


512 


PRACTICAL  MARINE  ENGINEERING. 


in  Fig.  286,  is  prepared  on  thick,  uniform  paper,  and  then  cut 
carefully  out  with  a  sharp-pointed  penknife. 

(3)  This  is  weighed  on  delicate  scales,  and  also  balanced  on 
the  knife  edge,  the  line  AB  containing  the  center  of  gravity  be- 
ing thus  found. 

(4)  A  square  of  the  paper  containing  any  convenient  num- 
ber, say  100  square  inches  of  area,  is  also  cut  out  and  weighed. 
This  divided  by  the  area  will  give  the  weight  of  the  paper  per 
square  inch. 

(5)  The  weight  of  the  paper  half  section  is  divided  by  that 


Fig.  286.    Volume  of  Piston  by  Rule  of  Pappus. 

of  the  square  inch.    The  quotient  will  be  the  area  of  the  paper 
half  section  in  square  inches. 

(6)  This  area  is  multiplied  by  the  square  of  the  scale  ratio  of 
the  drawing.    Thus  if  the  drawing  is  to  a  scale  I  inch  =  I  foot, 
it  is  in  the  ratio  i  :  12  with  the  original,  and  we  multiply  by 
12  X  12  or  144.    If  the  scale  is  i^  inches  =  i  foot  it  is  i  :  8,  and 
we  multiply  by  64.    If  to  a  scale  of  3  inches  =  i  foot  it  is  i  :  4 
and  we  multiply  by  16.    The  result  thus  found  will  be  the  area  of 
the  actual  full-sized  half  section  in  square  inches. 

(7)  We  then  multiply  the  distance  AG  scaled  off  according 
to  the  scale  of  the  drawing  and  expressed  in  inches,  by  6.2832, 
and  the  product  by  the  area  as  found  in  (6).    The  result  will  be 
the  volume  in  cubic  inches. 


SPECIAL   TOPICS   AND   PROBLEMS.  513 

Instead  of  the  preceding,  we  may  less  accurately  find  the 
area  by  taking  it  in  parts  and  using  substituted  simpler  forms,  as 
above  explained.  We  may  then  by  judgment  assume  the  loca- 
tion of  G  and  then  proceed  as  above  in  (7). 

Thus,  for  example,  suppose  we  find  as  follows : 
Scale  of  drawing  il/2  inches  =  i  foot. 
Weight  of  paper  section  240  grains. 
Weight  of  paper  per  square  inch  36  grains. 
Arm  AG  —  1.7  inches  on  the  paper  or  13.6,  as  scaled  from  the 

drawing. 

Then  area  =.  240  -=-  36  =  6.67  inches. 
This  multiplied  by  64  gives  426.7  square  inches  as  the  area  of  the 

actual  half  section. 
Then  volume  —  13.6  X  6.2832  X  426.7  =  36462  cubic  inches. 


514  PRACTICAL  MARINE  ENGINEERING. 


CHAPTER  X. 

PROPULSION  AND  POWERING. 


Sec.  78.  MEASURE  OF 

For  measuring  the  speed  of  steamships  the  customary  unit 
is  the  knot.  While  this  term  is  often  used  as  a  distance,  it  is 
really  a  speed  or  velocity.  As  adopted  by  the  United  States 
Navy  Department,  it  is  a  speed  of  6080.27  ft.  per  hr.  The  Brit- 
ish Admiralty  knot  is  a  speed  of  6080  ft.  per  hr.  For  all  ordi- 
nary purposes  the  United  States  and  British  knots  may  be  con- 
sidered the  same.  It  is  often  necessary  to  reduce  knots  to  feet 
per  minute  or  vice  versa.  To  this  end  we  divide  6080  by  60  and 
find  101.33  ft.  per  minute  as  the  equivalent  of  one  knot.  Hence 
the  following  rules  : 

To  reduce  knots  to  feet  per  minute  multiply  by  101.33. 

To  reduce  feet  per  minute  to  knots,  divide  by  101.33. 

In  the  inland  waters  of  the  United  States,  and  to  some  ex- 
tent on  the  coast  for  tugs,  yachts,  launches,  etc.,  the  mile  per  hour 
is  used  as  the  unit,  instead  of  the  knot.  A  statute  mile  consists 
of  5,280  feet.  Hence  one  mile  per  hour  equals  5,280  -r-  60,  or  88 
feet  per  minute.  Hence  : 

To  reduce  miles  per  hour  to  feet  per  minute,  multiply  by  88. 

To  reduce  feet  per  minute  to  miles  per  hour,  divide  by  88. 

Also: 

To  reduce  miles  per  hour  to  knots,  divide  the  former  by 

I5. 

To  reduce  knots  to  miles  per  hour,  multiply  the  former  by 


Sec.  79.  PROPULSION. 

To  propel  a  ship  through  the  water  some  kind  of  a  propul- 
sive thrust  must  be  obtained.  This  is  the  fundamental  problem 
of  propulsion.  Thus  when  a  boat  is  poled  along  a  shallow  creek 


PROPULSION  AND  POWERING.  515 

the  thrust  is  obtained  as  a  reaction  from  the  bed  of  the  creek 
against  the  end  of  the  pole  and  thence  to  the  man  who  is  pushing 
it,  and  thence  to  the  boat. 

In  the  usual  case,  however,  there  is  no  bottom  to  be 
reached,  and  the  only  thing  outside  the  ship  which  can  be  gotten 
hold  of  for  the  purpose  of  gaining  a  reaction  is  the  air  or  the 
water.  For  all  cases  with  which  the  engineer  is  concerned  it 
comes  to  the  latter,  and  so  the  problem  is  to  get  from  the  water 
a  reaction  or  force  directed  forward  by  means  of  which  the  ship 
maybe  pushed  through  the  water.  To  understand  how  this  is 
possible  we  must  remember  the  property  of  inertia,  one  of  the 
fundamental  properties  of  matter.  It  is  this  property  which  en- 
ables all  matter  to  resist  any  effort  made  to  change  its  condition 
bf  rest  or  relative  motion,  and  to  react  back  on  the  means  by 
which  such  a  change  is  effected.  Thus  a  push  of  the  hand  may 
serve  to  set  in  motion  a  weight  hanging  by  a  rope,  but  while  the 
condition  of  rest  is  being  overcome  the  weight  will  react  back  on 
the  hand  with  a  force  equal  and  opposite  to  that  which  the  hand 
exerts  upon  the  weight.  Similarly,  when  a  shot  is  fired  from  a 
gun,  the  inertia  of  the  shot  causes  it  to  react  back  against  the 
£as  and  so  to  the  gun,  causing  the  well  known  recoil. 

From  the  fundamental  principles  of  mechanics  it  follows 
that  to  obtain  a  thrust  or  reaction  forward  it  is  only  necessary  to 
produce  in  a  certain  mass  of  water  an  increase  in  velocity,  such 
increase  being  directed  from  forward  aft,  or  at  least  having  a 
component  in  that  direction.  There  will  then  be  a  reaction 
directed  from  aft  forward,  or  having  a  component  in  that  direc- 
tion, and  such  reaction  exerted  on  the  means  used  to  produce  the 
change  of  velocity  may  be  utilized  as  a  propulsive  thrust. 

This  is  carried  out  in  practice  by  either  a  screw  propeller  or 
paddle  wheel,  and  remembering  the  principles  above  stated,  it 
appears  that  the  immediate  purpose  of  the  propeller  or  paddle 
wheel  is  simply  to  produce  an  increase  in  the  velocity  of  the 
water  directed  from  forward  aft.  In  consequence  of  this  the 
water  will  exert  a  forward  reaction  on  the  propeller  or  paddle 
wheel,  and  thus  produce  the  thrust  required  to  propel  the  ship 
through  the  water.  It  may  be  added  that  this  increase  of  ve- 
locity from  forward  aft,  referred  to  above,  may  be  obtained  either 
by  taking  hold  of  water  at  rest  and  giving  it  a  motion  stern  ward, 
by  taking  hold  of  water  already  moving  stermvard  and  giving  it 
a  still  higher  velocity  in  the  same  direction,  or  by  taking  hold  of 


PRACTICAL  MARINE  ENGINEERING. 


PROPULSION  AND  POWERING.  5*7 

water  moving  forward  and  decreasing  such  forward  motion, 
stopping  it  and  leaving  it  at  rest,  or  reversing  it  to  a  sternward 
motion.  In  all  cases  it  is  the  change  of  velocity  which  is  of  im- 
portance. Thus  a  change  from  rest  to  5  feet  per  second  aft,  or 
from  3  feet  per  second  aft  to  8  feet  per  second  aft,  or  from  5  feet 
per  second  forward  to  rest,  or  from  2  feet  per  second  forward  to 
3  feet  per  second  aft,  will  each  give  the  same  forward  thrust. 

We  shall  not  go  further  into  the  theory  of  propulsion,  but  in 
the  next  section  will  give  certain  definitions  relating  to  screw 
propellers  and  the  solution  of  a  few  simple  problems. 


Sec.  80.  SCREW 

[i]  Definitions. 

A  screw  propeller  as  shown  in  the  frontispiece  and  in  Figs. 
287,  288,  consists  of  a  hub  and  a  certain  number  of  blades, 
usually  two,  three  or  four.  The  blades  have  on  their  rear  or 
driving  side  an  approximately  helical  surface  —  that  is,  a  surface 
similar  to  that  which  forms  the  faces  of  an  ordinary  screw  thread. 
In  this  view  a  two-bladed  screw  propeller  may  be  considered  as 
a  small  part  of  a  double-threaded  bolt,  the  threads  being  cut  very 
deep,  and  all  portions  being  cut  away  down  to  the  hub  except 
the  parts  retained  for  blades.  Similarly  a  three  or  four-bladed 
propeller  may  be  considered  as  a  small  part  of  a  triple  or  quad- 
ruple-threaded bolt  similarly  cut  away  except  for  the  parts  re- 
tained for  blades. 

The  hub  or  boss  is  the  central  portion  to  which  the  blades  are 
attached,  and  through  which  they  receive  their  motion  of  rota- 
tion in  a  transverse  plane  relative  to  the  ship. 

A  propeller  is  said  to  be  right  hand  or  left  hand,  according 
as  it  turns  with  or  against  the  hands  of  a  watch  when  looked  at 
from  aft  and  driving  the  ship  ahead. 

The  face  or  driving  face  of  a  blade  is  to  the  rear.  It  is  that 
face  which  acts  on  the  water  and  so  receives  the  forward  thrust. 

The  back  of  a  blade  is  therefore  on  the  forward  side.  Care 
must  be  taken  not  to  confuse  these  terms. 

The  leading  and  following  edges  of  a  blade  are  respectively 
the  forward  and  after  edges. 

The  diameter  of  a  propeller  is  the  diameter  of  the  circle 
swept  by  the  tips  of  the  blades. 

The  pitch  of  a  propeller  is  the  same  as  the  pitch  of  the  screw 
thread,  of  which  it  may  be  considered  as  forming  a  small  part  — 


518 


PRACTICAL  MARINE  ENGINEERING. 


that  is,  it  is  the  longitudinal  distance  between  the  successive  turns 
of  the  helical  surface.  This  definition  will  hold,  however,  only 
when  the  pitch  is  the  same  over  the  entire  face  of  the  blade.  In 
many  cases  the  pitch  varies  from  one  point  to  another,  and  we 
must  therefore  understand  the  term  as  relating,  in  such  cases, 
to  a  small  element  of  the  driving  face  only.  From  this  view  the 
pitch  may  be  defined  as  the  longitudinal  distance  which  the  ship 
would  be  driven  for  one  revolution  were  this  element  to  work 


Fig.  288.     Screw  Propeller,,  Detachable  Blades. 

on  a  smooth,  unyielding  surface,  as,  for  example,  the  cor- 
responding surface  of  a  fixed  nut.  The  pitch  thus  defined  will 
depend  on  the  location  and  inclination  of  the  surface  at  the  point 
or  element  considered,  and  its  value  may  thus  vary  from  one 
point  to  another  over  the  entire  face  of  the  blade.  The  pitch  is 
thus  said  to  be  uniform  or  variable,  as  its  value  remains  the  same 
or  changes  from  point  to  point  over  the  driving  face.  If  it  in- 
creases as  we  go  from  the  hub  to  the  tip  of  the  blade  it  is  said  to 


PROPULSION  AND  POWERING.  519 

increase  radially.  If  it  is  greater  on  the  following  than  on  the 
leading  edge,  it  is  said  to  increase  axially.  The  latter  is  usually 
implied  by  the  simple  term  increasing  or  expanding  pitch. 

The  pitch  ratio  is  the  pitch  divided  by  the  diameter,  or  the 
ratio  of  pitch  to  diameter. 

The  area,  developed  area  or  helicoidal  area  of  a  blade  is  the 
actual  surface  of  the  driving  face.  For  the  propeller  as  a  whole 
it  is  the  sum  of  the  areas  of  all  the  blades. 

The  projected  area  is  likewise  the  area  of  the  projection  on 
a  transverse  plane,  of  one  blade  or  of  all  the  blades  collectively. 

The  disk  area  is  the  area  of  the  circle  swept  by  the  tips  of 
the  blades. 

The  pitch  has  been  defined  as  the  distance  which  the  pro- 
peller in  one  revolution  would  drive  the  ship  if  it  worked  on  a 
smooth,  unyielding  surface.  Instead  of  working  on  such  a  sur- 
face, however,  the  propeller  works  on  the  water,  a  yielding  me- 
dium, and  in  consequence  the  water  recedes  somewhat  under  the 
action  of  the  propeller  and  the  ship  moves  forward  per  revolu- 
tion a  distance  less  than  the  pitch.  The  difference  between  the 
pitch  and  the  distance  the  ship  actually  moves  per  revolution  is 
called  the  slip,  or,  more  concisely,  the  slip  per  revolution.  The 
ratio  of  this  slip  to  the  pitch  is  called  the  slip  ratio,  or  simply  the 
slip  stated  in  per  cent  as  a  slip  of  20  per  cent,  30  per  cent,  etc. 

Let  p  denote  the  pitch  of  the  propeller  in  feet. 
N     "         "  revolutions  per  minute. 
u      "          '  velocity  of  the  ship  in  knots. 
^       "         "  slip  ratio. 

Then  101.3  »  -r-  AT  is  the  distance  traveled  by  the  ship  per 
revolution,  and  p  —  (101.3  w  —  N)  is  the  slip  per  revolution. 
Hence  for  the  slip  ratio  we  have  : 

101.3  " 


Multiplying  both  terms  of  the  fraction  by  ^V  we  have: 

AY-  ""-a  K  ,. 

~~pN~ 

The  term  pN  is  the  distance  the  ship  would  go  per  minute  if 
there  were  no  slip,  while  101.3  «  is  the  distance  which  is  actually 
made  good.  The  difference  or  pN  —  101.3  u  may  therefore  be 
called  the  slip  per  minute,  and  the  quotient  of  this  by  /\Y  is  the 


520  PRACTICAL  MARINE  ENGINEERING. 

slip  ratio.     This  latter  equation  for  ^  is  the  one  by  means  of 
which  its  value  is  usually  computed. 

It  may  be  well  to  note  at  this  point  that  while  slip  implies  a 
certain  loss  of  effectiveness  in  the  propeller,  it  is  a  loss  which  is 
necessary  in  the  very  nature  of  the  case.  We  have  already  seen 
that  to  obtain  a  propulsive  thrust  we  must  give  to  a  certain  body 
of  water  an  increased  velocity  sternward.  This  means  that  the 
water  must  yield  under  the  action  of  the  propeller,  and  it  is  this 
yielding  or  falling  sternward  which  thus  gives  rise  at  the  same 
time  to  both  the  slip  and  the  propulsive  thrust.  We  cannot 
therefore  have  the  thrust  without  the  slip:  we  must  accept  the 
latter  to  obtain  the  former. 

We  must  now  introduce  a  further  consideration.  We  have 
defined  slip  as  the  difference  between  the  pitch  on  the  driving 
face  and  the  advance  per  revolution.  The  latter  admits  of  being 
defined  in  two  ways  according  as  we  take  for  our  point  of  refer- 
ence a  point  in  the  outlying  still  water,  or  a  point  in  the  water 
about  the  stern  of  the  ship  and  in  which  the  propeller  works.  So 
far  as  we  are  concerned  with  the  movement  of  the  ship  through 
the  water  as  a  whole,  the  former  is  the  natural  point  of  reference. 
For  various  considerations  connected  with  the  operation  of  the 
propeller  itself,  however,  the  latter  is  the  more  important.  Let 
us  note  briefly  the  condition  of  the  water  close  about  the  stern  of 
the  ship  and  in  which  the  propeller  works. 

The  ship  in  moving  through  the  water  will  throw  into  for- 
ward motion  a  skin  of  water  extending  from  the  surface  of  the 
ship  for  several  inches  outward.  Very  near  the  surface  of  the 
ship  this  will  move  with  nearly  the  velocity  of  the  ship,  while  as 
the  distance  from  the  surface  is  increased  the  velocity  will  rap- 
idly decrease  and  soon  become  insensible.  The  water  thus  given 
forward  motion  by  the  skin  of  the  ship  will  finally  be  found  at 
the  stern,  where,  still  further  influenced  by  wave  and  stream  line 
motion,  it  forms  the  so-called  "wake."  The  forward  velocity  in 
the  wake  at  different  points  in  a  transverse  plane  at  the  stern  is 
quite  irregular,  rising  as  high  as  50  to  75  per  cent  of  that  of  the 
ship  at  points  near  the  surface  and  near  the  stern  post,  and  de- 
creasing irregularly  and  gradually  to  nothing  at  the  outlying  still 
water.  For  single  screw  ships  the  average  value  in  that  part  of 
the  wake  directly  influenced  by  the  screw  is  usually  from  10  to 
20  per  cent  of  the  speed  of  the  ship.  For  twin  screws  located 
somewhat  aside  from  the  strongest  part  of  the  wake  the  values 


PROPULSION  AND  POWERING.  521 

are  usually  found  between  6  and  12  per  cent  of  the  speed  of  the 
ship. 

Now  with  reference  to  the  propeller,  it  is  evident  that  so  far 
as  it  is  concerned  individually  and  as  an  appliance  for  developing 
thrust,  it  should  be  judged  relative  to  the  water  immediately 
about  it  and  in  which  it  works  rather  than  relative  to  an  outly- 
ing body  of  undisturbed  water  upon  which  it  has  no  direct  influ- 
ence. The  slip  which  is  given  by  taking  the  speed  relative  to  the 
wake  is  therefore  called  the  true  slip,  while  that  given  by  taking 
the  speed  relative  to  the  outlying  still  water  (the  speed  as  usually 
considered)  is  called  the  apparent  slip. 

To  show  the  relation  between  the  true  and  apparent  slips  let 
v  denote  the  forward  velocity  of  the  wake  and  u  that  of  the  ship 
as  before,  both  measured  in  knots  and  relative  to  the  outlying 
still  water.  Then  (u  —  v)  is  the  speed  of  the  advance  of  the  pro- 
peller through  or  relative  to  the  wake.  Also  using  the  same  no- 
tation as  above, 

p  N —  101.3  (u  —  v)  is  the  true  slip  per  minute,  while,  as  before, 
'p  N —  101.3  u  is  the  apparent  slip  per  minute.  Denoting  the  lat- 
ter by  5"i,  and  the  former  5"*,  we  have : 

Si  =  p  N —  101.3  u. 

S*  =  p  N —  101.3  (u  —  v)  =  5"i  +  101.3  v. 

It  thus  appears  that  the  difference  between  the  two  slips  in 
feet  per  minute  is  simply  the  wake  velocity,  as  we  should  expect. 

To  reduce  to  slip  ratio  we  use  pN  as  the  divisor  in  each  case, 
and  denoting  the  resulting  ratios  by  si  and  s*  we  have  : 

pN  —  101.3  u  . 

st  =  —  -  -  as  before,  and: 

pN 

fN—i6i*3(u  —  v)  101.3 v 

~pN~  =  S*  +        pjy 

Where  the  term  slip  is  used  without  special  definition,  the 
apparent  slip  is  usually  intended. 

In  the  preceding  discussion  of  slip  we  have  used  the  term 
pitch  as  though  it  were  of  constant  value  over  the  entire  surface 
of  the  blade.  If  such  is  not  the  case,  then  the  term  must  be  un- 
derstood as  referring  to  a  mean  or  average  value.  Such  an  aver- 
age value  of  the  pitch  of  a  propeller  might  be  defined  in  a  variety 
of  ways,  but  engineers  are  not  as  yet  agreed  upon  the  method 
most  suitable.  This  point,  however,  is  one  which  cannot  be  fur- 
ther developed  in  the  present  work. 


522  PRACTICAL  MARINE  ENGINEERING. 

Problems. 

(1)  To  find  the  apparent  slip. 

From  the  preceding  value  of  the  apparent  slip  ratio  s  we 
may  derive  the  following  : 

Rule  :  —  (i)  Multiply  the  pitch  by  the  revolutions  per 
minute. 

(2)  Multiply  the  speed  in  knots  by  101.3. 

(3)  Subtract  the  result  in  (2)  from  that  in  (i)  and  divide  the 
difference  by  the  result  in  (i).    The  quotient  will  be  the  slip  ratio. 

Example  :    Given  speed  of  ship,  1  1  knots  ;  pitch,  20  feet  ; 
revolutions,  72.    Find  the  apparent  slip. 
Operation  :  20  X  72  =  1440. 

ii  X  101.3=1114.3. 

1440  —  1114-3  -i-  1440  =  3257  -=-  J440  =  22.6    per 
cent,  ans. 

(2)  To  find  the  speed,  having  given  the  other  items. 

From  the  preceding  equation  we  derive  the  following  value 
for  u: 

u  .  >"  ('  -  '>  (,) 

101.3 

Whence  the  following  : 
Rule:  —  (i)  Multiply  the  pitch  by  the  revolutions. 

(2)  Subtract  the  slip  per  cent  from  i  .00. 

(3)  Multiply  the  result  in  (i)  by  that  in  (2). 

(4)  Divide  the  result  in  (3)  by  101.3.    The  quotient  will 
be  the  speed  in  knots. 

Example:   Given  pitch,  18  feet;  revolutions,  no;  apparent 
slip,  18  per  cent.    Find  the  speed. 
Operation  :   18  X  no  =  1980. 

i.oo  —  .18  =  .82. 

.82  X  1980  =  1624. 

1624  -T-  101.3  =  16.03  knots,  ans. 

(3)  To  find  the  revolutions,  having  given  the  other  items. 
From  the  preceding  equation  we  derive  the  following  value 

for  N: 

,,  101.^  U 

*  ' 


The  use  of  this  formula  will  be  illustrated  by  the  following 
example  : 

Given  speed,  22  knots;  pitch,  26  feet;  apparent  slip,  16  per 
cent.  Find  revolutions. 


PROPULSION  AND  POWERING.  '  523, 

Operation  :  101.3  X  22  =  2228.6 

(1.00— .16)  X  28  =  23.52 

2228.6  -f-  23.52  =  94.8  revolutions  per  minute,  ans. 
(4)  To  find  the  pitch,  having  given  the  other  items. 
From  the  preceding  equation  we  derive  the  following  value 
for  p. 

101.3  if 

P    -  -N(i—s)  <4> 

The  use  of  this  formula  will  be  illustrated  by  the  following 
example : 

Given  speed,  28  knots;  apparent  slip,  21  per  cent;  revolu- 
tions, 380.    Find  the  corresponding  pitch. 
Operation  :  101.3  X  28  =  2836.4 

380  X  (i.oo  —  .21)  =  300.2 
2836.4  -4-  300.2  =  9.45  feet,  ans. 

[3]  Varieties  of  Propellers. 

Screw  propellers  are  found  in  the  greatest  variety  according 
to  the  number,  shape,  style  and  arrangement  of  blades.  In  mod- 
ern practice  the  number  of  blades  is  usually  either  three  or  four, 
the  former  being  perhaps  more  commonly  met  with  in  twin 
screws  and  the  latter  in  single  screws. 

The  shape  of  the  blades  may  be  oval  or  elliptical,  as  in  Figs. 
287,  288,  or  broadening  somewhat  toward  the  tip  with  rounded 
corners,  or  of  any  intermediate  or  similar  form  which  may  be 
desired.  The  oval  or  generally  rounded  form  of  blade  is  most 
commonly  met  with  in  modern  practice.  The  blades  may  also 
be  bent  or  curved  in  various  ways.  Thus  in  propellers  for  small 
boats  the  blades  are  often  bent  back,  as  in  Fig.  287,  so  as  to 
throw  them  somewhat  farther  from  the  stern  post.  They  are 
also  sometimes  curved  in  the  plane  of  rotation  so  that  the  en- 
tering edge  is  well  rounded  as  it  enters  the  water  in  going- 
ahead.  Combined  with  these  there  may  be  various  modifications 
of  pitch,  as  above  referred  to.  The  normal  or  standard  pro- 
peller in  modern  practice  may,  however,  be  considered  as  one 
having  plain  blades  of  uniform  pitch,  of  oval  or  elliptical  form, 
and  standing  at  right  angles  to  the  axis,  as  in  Fig.  288.  Most 
of  the  variations  from  this  type  are  based  on  fancy  rather  than 
on  definite  engineering  reasons.  So  far  as  is  known  at  present, 
the  simple  normal  type,  as  specified  above,  is  the  equal  of  any 
of  those  of  variable  pitch  or  of  special  form  or  shape  of  blade. 


524  PRACTICAL  MARINE  ENGINEERING. 

and  while  it  may  be  that  some  special  combination  of  pitch, 
shape  and  form  of  blade  may  give  a  higher  efficiency  than  can  be 
obtained  from  the  normal  type,  yet  up  to  the  present  time  such 
results  have  not  been  proven. 

Small  propellers  are  usually  made  complete  or  in  one  cast- 
ing, as  in  Fig.  287.  Large  propellers  are  made  either  in  one 
casting  or  with  separate  or  sectional  blades,  as  in  Fig.  288.  In 
the  latter  case  the  root  of  the  blade  carries  a  circular  flange  fit- 
ting into  a  corresponding  recess  in  the  hub.  This  serves  to  se- 
cure the  blade  to  the  hub  by  stud-bolts  passing  through  the 
flange  and  fitted  with  nuts  countersunk  below  its  outer  face. 
The  general  details  of  this  arrangement  are  shown  in  the  figure. 
The  holes  in  the  flanges  are  usually  made  slightly  oblong,  thus 
providing  for  a  slight  change  in  the  pitch  by  turning  the  flange 
back  and  forth,  and  thus  changing  the  average  obliquity  of  the 
blade  to  the  axis  of  the  propeller.  Once  adjusted  as  desired  the 
holes  are  filled  by  packing  pieces  so  that  no  further  change  can 
result  from  the  accidental  slipping  of  the  flange  under  the  nuts. 
In  this  connection  it  may  be  noted  that  the  change  of  pitch  re- 
sulting from  such  a  twisting  of  the  blade  is  not  the  same  for  all 
parts  of  the  blade,  but  varies  from  root  to  tip.  It  follows,  if  the 
blade  is  made  of  uniform  pitch,  that  it  will  remain  so  only  sa 
long  as  it  is  set  at  the  corresponding  angle,  and  that  if  it  is 
twisted  to  and  fro  the  pitch  will  be  increased  and  decreased,  but 
not  uniformly ;  so  that  in  all  positions  but  this  one  the  pitch  will 
no  longer  be  uniform,  but  variable.  For  a  moderate  angle  of 
twist,  however,  the  change  from  uniformity  is  but  slight,  and 
changes  of  average  pitch  up  to  perhaps  10  to  15  per  cent  may  be 
made  without  serious  departure  from  the  average. 

The  chief  advantages  of  the  separate  blades  lie  in  the  possi- 
bility of  varying  or  adjusting  the  pitch  as  just  described,  and  in 
the  readiness  with  which  repairs  may  be  executed.  A  separate 
blade  broken  or  defective  may  be  .readily  removed  and  replaced 
with  a  new  one,  this  operation  in  small  vessels  being  sometimes 
accomplished  without  placing  the  vessel  in  dry  dock.  One  or 
two  blades  may  also  be  carried  as  spare  parts  or  shipped  by  rail, 
or  otherwise,  much  more  readily  than  an  entire  propeller. 

The  attachment  of  the  propeller  to  the  shaft  is  shown  by  the 
figures.  The  taper  is  usually  about  I  inch  in  the  diameter  per 
foot.  The  propeller  is  prevented  from  turning  on  the  shaft  by 
one  or  more  keys  fitted,  as  shown.  The  after  end  of  the  shaft 


PROPULSION  AND  POWERING.  525 

is  fitted  with  a  nut  which  serves  to  hold  the  propeller  against 
any  tendency  to  slip  off  when  backing,  and  this  is  often  covered 
with  a  conical  tail  piece,  as  shown,  in  order  to  reduce  the  eddy 
formation  just  aft  of  the  boss.  It  may  be  noted  that  for  a  right- 
hand  propeller  the  nut  is  usually  left  hand,  and  vice  versa,  it  be- 
ing considered  that  this  arrangement  reduces  the  liability  of 
loosening  or  backing  off. 

If  water  is  allowed  to  come  into  contact  with  the  taper  of 
the  shaft  on  which  the  propeller  boss  is  secured  it  may  give  rise 
to  considerable  corrosion,  and  this  may  set  the  boss  so  firmly  on 
the  shaft  that  great  difficulty  will  be  experienced  in  its  removal. 
In  order  to  prevent  the  contact  of  water  with  the  taper,  various 
means  may  be  employed.  In  one  method  the  brass  liner  on  the 
shaft  is  carried  along  nearly  to  the  forward  end  of  the  taper,  and 
a  rubber  ring  is  placed  just  forward  of  the  boss  or  in  a  counter- 
bore.  As  the  boss  is  forced  on,  the  rubber  ring  is  compressed 
between  the  boss  and  the  liner,  and  thus  a  water-tight  joint  is 
made.  See  Fig.  288.  In  other  cases  the  liner  is  carried  into  a 
counterbore  in  the  boss  and  a  red  lead  joint  is  made  between 
the  two. 

For  the  examination  or  repair  of  the  stern  bearing  it  may 
become  necessary  to  remove  the  propeller  and  withdraw  the  tail 
shaft  forward  into  the  ship.  This  is  of  course  an  operation  re- 
quiring the  docking  of  the  ship.  For  the  removal  of  the  pro- 
peller the  first  attempt  may  be  made  with  steel  wedges  between 
the  forward  face  of  the  boss  and  the  stern  post,  or  after  end  of 
the  stern  bearing.  The  space  between  the  two  is  made  up  with 
the  metal  blocking  necessary,  and  the  wedges  are  then  inserted 
and  driven  one  from  either  side.  In  this  way  a  tremendous 
strain  can  be  exerted  and  the  boss  will  be  started  unless  seriously 
corroded  or  jammed  unduly  tight.  In  the  latter  cases  recourse 
must  be  had  to  hydraulic  jacks,  or  to  a  heavy  ram  or  to  heating 
the  boss  in  order  to  expand  it  in  size  and  break  the  connection 
with  the  shaft.  Once  the  boss  is  started  the  weight  of  the  pro- 
peller may  be  taken  by  chain  hoists  suspended  from  the  counter, 
and  the  shaft  may  then  be  drawn  forward  into  the  tunnel. 

In  the  case  of  twin  screw  ships  with  the  common  form  of 
strut,  the  same  general  means  may  be  employed,  except  that  it 
should  be  remembered  that  the  strain  set  up  is  carried  on  the 
strut,  and  the  means  taken  should  not  go  so  far  as  to  endanger 
its  rupture  or  the  undue  straining  of  its  fastenings. 


526  PRACTICAL  MARINE  ENGINEERING. 

[3]  Materials. 

Cast  iron,  cast  steel,  brass,  gun  metal  and  the  various  bronzes 
are  the  materials  used  for  screw  propellers.  Cast  iron  is  the 
cheapest,  but  is  relatively  weak  and  brittle,  and  the  blades  must 
necessarily  be  thicker  and  less  efficient  than  if  made  of  steel  or 
bronze.  Cast  steel  is  stronger  than  cast  iron,  and  the  sections 
may  be  accordingly  decreased  with  a  resultant  gain  in  efficiency. 
The  surface  of  cast  steel  is  naturally  not  as  smooth  as  with  cast 
Iron,  but  with  improved  methods  of  production  the  difference  is 
not  important.  Brass  and  the  various  bronzes  have  naturally 
a  smoother  surface,  and  seem  furthermore  to  have  a  lower  co- 
efficient of  skin  resistance.  This,  added  to  their  strength  and 
good  casting  qualities,  makes  possible  a  smooth  and  relatively 
thin  blade  with  sharp  edges,  all  of  which  are  features  favorable 
to  good  efficiency.  With  the  best  bronzes  the  ultimate  strength 
may  vary  from  50,000  to  60,000  pounds  per  square  inch  of  sec- 
tion. With  cast  steel  the  ultimate  strength  will  reach  still  higher, 
or,  say,  to  65,000  pounds  per  square  inch.  With  gun  metal  an 
ultimate  strength  of  25,000  to  35,000  pounds  may  be  expected, 
while  with  common  brass  and  cast  iron  not  more  than  20,000  to 
25,000  pounds  can  be  depended  on. 

Of  the  various  materials  available,  manganese  bronze  may 
perhaps  be  considered  as  possessing  the  best  combination  of 
desirable  qualities,  such  as  strength  and  stiffness,  good  casting 
qualities,  resistance  to  corrosion,  etc.  Care  is  needed  in  the 
manipulation  of  the  various  bronzes  in  melting,  pouring  and 
cooling,  in  order  to  insure  uniformity  and  the  full  realization  of 
the  valuable  properties  of  the  alloy.  The  greater  cost  of  such 
bronzes  restricts  their  use,  however,  to  warships,  yachts  and 
launches,  ocean  liners  and  other  cases  where  the  importance  of 
a  saving  in  propulsive  efficiency  may  be  considered  worth  the  in- 
creased cost  of  the  propeller. 

The  durability  of  propeller  blades  is  usually  in  the  order: 
bronze,  cast  iron,  cast  steel.  The  two  latter  usually  suffer  by 
general  corrosion  and  local  pitting,  the  average  life  being  usually 
from  five  to  ten  years.  The  life  of  bronze  blades  is  practically 
indefinite. 

[4]  Measurement  of  Pitch. 

To  determine  the  pitch  of  a  given  propeller  three  measure- 
ments are  necessary.  See  Fig.  289.  These  are  : 

(i)  The  radius  OA  at  which  the  pitch  is  desired. 


PROPULSION  AND  POWERING. 


527 


(2)  The  angle  or  part  of  the  complete  circumference  cor- 
responding to  the  distance  on  the  blade  between  A  and  B,  the 
two  points  between  which  the  pitch  is  to  be  found. 

(3)  The  advance  BC  parallel  to  the  line  of  the  shaft,  corre- 
sponding to  this  part  of  a  complete  revolution. 

In  the  figure,  A  and  B  are  points  on  the  face  of  the  blade, 
and  are  at  a  constant  distance  OA  from  the  shaft  center  line  OO. 
AC  is  an  arc  of  a  circle  which  lies  in  a  plane  through  A  and  per- 
pendicular to  the  shaft.  The  angle  AOC  is  therefore  the  one  re- 
ferred to  in  (2),  and  the  distance  BC  is  the  corresponding  ad- 
vance. Then  BC  is  the  same  fraction  of  the  entire  pitch  that 
AOC  is  of  a  complete  circle,  or  the  same  fraction  that  the  length 


Fig.  289.     Measurement  of  Pitch. 

AC  is  of  a  complete  circumference  with  OA  as  radius.  This 
complete  circumference  will  be  6.2832  X  OA.  Hence  the  pro- 
portion : 

AC  :  6.2832  X  OA  :  :  BC  :  pitch. 

6.2832  x  OA  x  BC 


or  pitch  — 


AC 


It  is  not,  however,  as  easy  to  measure  AC  as  AB,  so  that 
we  may  put  for  AC  its  equal  j/  ^-g  *_  p^.and  we  then  have 

pitch  ==  1^3*_x.OAjLgC 


AB2-    h'C2 
A  brief  outline  of  the  operations  is  as  follows : 


52S  PRACTICAL  MARINE  ENGINEERING. 

(1)  Select  the  points  A  and  B  at  and  between  which  the 
pitch  is  desired,  making  sure  that  they  are  at  equal  distances 
from  the  shaft  center  line.    This  can  be  done  by  squaring  down 
from  a  straight  edge  or  other  reference  line  PQ,  PR,  placed 
across  the  hub  and  at  right  angles  with  the  shaft.    Then  measure 
the  length  AB. 

(2)  The  propeller  being  leveled  up,  measure  the  distance 
BC  from  a  level  through  A  vertically  down  to  B.    Or  if  the  pro- 
peller cannot  be  leveled,  measure  from  B  in  a  direction  parallel 
to  the  shaft  out  to  a  line  through  A  in  a  plane  at  right  angles  to 
the  shaft.    Or  measure  from  Q  down  to  A  and  from  R  down  to 
B  and  take  their  difference  BC. 

(3)  Multiply  the  distance  OA  or  its  equal  PQ  by  6.2832,  and 
by  the  length  BC  all  in  the  same  units  of  measure. 

(4)  Square  the  lengths  AB  and  BC,  subtract  the  square  of 
the  latter  from  that  of  the  former  and  extract  the  square  root 
of  the  difference. 

(5)  Divide  the  result  found  in  (3)  by  that  found  in  (4)  and 
the  quotient  will  be  the  pitch  desired. 

Thus,  for  example,  suppose 

AB  =  20  inches,  BC  =  13  inches  and  OA  =  48  inches. 

Then  6.2832  X  48  X  13  —  392Q-7 

AlSO     1/400    —     169    -    1/237  =:    15.2. 

Then  3920.7  -f-  15.2  =  238  inches  =  21  ft.  6  in.  =  pitch. 

If  the  pitch  is  variable  instead  of  uniform,  the  operation  is 
precisely  the  same,  but  the  result  found  must  be  considered 
merely  as  the  mean  or  average  value  of  the  pitch  between  the 
points  A  and  B.  For  other  parts  of  the  blade  a  similar  process 
will  give  the  pitch  at  those  points. 

When  the  propeller  is  in  place  on  the  ship  it  is  sometimes 
more  convenient  to  carry  out  the  principles  involved  in  this 
method  of  measuring  pitch  somewhat  differently,  as  follows :  Let 
the  propeller  be  turned  so  as  to  bring  one  of  the  blades  horizon- 
tal. Then  select  the  place  at  which  the  pitch  is  desired,  and  hang 
over  the  blade  at  this  point  a  cord  with  two  weights,  as  shown  in 
Fig.  290.  Care  must  be  taken  that  the  two  points  A  and  B  at 
which  the  cord  touches  the  edges  of  the  blade  are  at  the  same 
distance  from  the  center.  It  is  then  readily  seen  that  the  points 
A  and  B  of  Fig.  290  correspond  to  the  similar  points  of  Fig.  289, 
except  that  in  Fig.  290  they  are  of  necessity  taken  on  the  ex- 
treme edges  of  the  blade.  We  then  level  up  a  bar  PQ  and  meas- 


PROPULSION  AND  POWERING. 


529 


ure  the  distances,  AB  and  BC,  as  noted  above,  using  them  in  the 
same  way  for  finding  the  pitch.  Or  we  may  measure  AC  directly 
and  use  this  with  BC  in  the  proportion  above. 

As  a  rough  and  ready  rule  it  may  be  remembered  that  the 
pitch  of  a  propeller  will  equal  the  length  of  a  circumference  at 
the  place  on  the  blade  where  the  slope  of  the  face  is  45°,  or  where 
it  is  equally  inclined  to  the  shaft  and  to  the  transverse  direction. 
Starting  near  the  shaft,  the  inclination  to  the  longitudinal  is 
small,  but  increases  toward  the  tip,  passing  at  some  point 
through  the  value  45°.  At  this  point  let  the  radius  be  r.  Then 


Marine  Enyinefri*g 

Fig.   290.     Measurement  of  Pitch. 


pitch  =  2  TIT  =  6.2832  r.  In  this  way  an  approximate  idea  may 
often  be  quickly  obtained  of  the  pitch  of  a  wheel  by  estimate 
without  special  measurement,  except  for  the  radius  or  diameter 
at  which  the  blade  has  the  slope  of  45°. 

The  details  of  the  above  methods  for  finding  pitch  may  vary 
considerably,  but  the  description  given  will  serve  to  show  the 
principles  involved,  and  with  reasonable  mechanical  skill  no 
trouble  will  be  found  in  carrying  out  the  measurements  required. 


Sec.  81.   PADDLE 

In  addition  to  the  screw  propeller  the  paddle  wheel  is  the 
other  appliance  used  for  ship  propulsion.  In  Fig.  291  is  shown 
in  skeleton  a  common  radial  paddle  wheel.  In  this  type  of 
wheel  the  paddles  or  floats  are  rigidly  fixed  to  the  arms,  the  lat- 


530 


PRACTICAL  MARINE  ENGINEERING. 


ter  being  connected  at  their  inner  ends  to  a  hub,  which  is  carried 
on  the  shaft.  In  this  manner  the  motion  of  the  shaft  is  transmit- 
ted to  the  floats,  and  these,  acting  on  the  water,  drive  it  stern- 
ward  and  thus  receive  the  forward  thrust  which  is  required  for 
the  propulsion  of  the  vessel. 

In  Fig.  292  is  shown  a  feathering  paddle  wheel.  In  this  ar- 
rangement the  floats  are  hung  on  axes  and  are  swung  in  such 
way  that  they  enter  and  leave  the  water  nearly  in  an  edgewise 
direction.  In  this  way  there  is  less  disturbance  of  the  water  and 
a  smoother  action  of  the  wheel  is  obtained.  Such  arrangement 
is  especially  suitable  for  ships  operating  under  widely  varying 
conditions  of  draft,  for  the  floats  of  a  deeply  immersed  radial 


Fig.  291.     Radial  Paddle  Wheel,  Skeleton  Diagram. 

wheel  enter  and  leave  the  water  at  a  great  obliquity  and  there 
would  be  considerable  loss  by  oblique  action. 

There  are  two  chief  methods  by  which  the  proper  motion 
may  be  given  to  feathering  floats,  depending  on  whether  the  pad- 
dle shaft  has  an  outer  or  spring  bearing  on  the  outside  of  the 
paddle  box  or  is  overhung ;  that  is,  provided  simply  with  a  bear- 
ing on  the  rail,  the  paddle  wheel  itself  being  then  mounted  on 
the  overhung  end  of  the  shaft.  In  the  former  case  the  arrange- 
ment will  be  understood  from  the  skeleton  drawing  of  Fig.  293. 
The  stationary  excentric  A  has  its  center  forward  of  the  wheel 
center,  as  shown.  To  the  excentric  strap  is  attached  a  drive  link 
HB,  connected  by  pin  joint  to  an  arm  BC,  carrying  a  float  DE. 


PROPULSION  AND  POWERING. 


53i 


532 


PRACTICAL  MARINE  ENGINEERING. 


The  other  floats,  mounted  in  a  similar  manner,  are  connected  by 
pin  joint  links  to  the  excentric  strap,  as  shown.  As  the  wheel 
turns  the  drive  link  HB  carries  the  strap  around  the  excentric 
sheave,  and  with  it  the  series  of  connected  links.  This  gives  a  see- 
saw motion  to  the  ends  of  the  arms  BC  and  thus  swings  the  floats 
in  the  manner  desired. 

When  the  paddle  shaft  has  no  outer  bearing,  as  in  the  ar- 
rangement shown  in  Fig.  292,  the  disc  carrying  the  links  may  be 
mounted  on  a  supporting  pin  carried  on  the  outer  side  of  the 
guard.  It  may  then  be  given  motion  through  a  drive  link  and 
connections,  as  shown,  giving  a  similar  see-saw  motion  to  the 
floats,  as  in  the  former  case. 

In  modern  practice  the  arms  of  paddle  wheels  are  made  of 


Fig.   .293.      Paddle   Wheel,    Skeleton   of   Arrangement   for  Feathering  Floats. 


steel,  the  hubs  of  cast  iron  or  cast  steel,  and  the  floats  of  wood 
or  boiler  plate ;  in  the  latter  case  often  curved  in  cross  section. 

In  estimating  the  pitch  of  the  paddle  wheel  or  what  corre- 
sponds to  pitch  in  the  screw  propeller,  we  must  consider  it  as  the 
circumference  of  the  circle  traveled  by  the  floats.  Since,  how- 
ever, a  float  as  a  whole  is  made  up  of  a  series  of  strips  or  ele- 
ments at  varying  distances  from  the  center,  each  such  element 
will  have  its  own  circumference  and  therefore  its  own  pitch,  arid 
will  try  to  drive  the  ship  at  a  speed  corresponding  to  such  pitch. 
The  paddle  wheel  as  a  whole  has  therefore  a  varying  pitch,  in- 
creasing from  the  outer  to  the  inner  edge  of  the  float.  The  re- 


PROPULSION  AND  POWERING.  533 

sultant  mean  pitch  is  considered  as  the  circumference  traveled  by 
a  point  called  the  center  of  effort.  The  proper  basis  for  the  deter- 
mination of  this  point,  and  hence  of  the  true  mean  pitch  of  a  pad- 
dle wheel  is,  however,  not  definitely  known,  and  can  only  be  de- 
termined by  the  aid  of  extended  experimental  investigation.  In 
the  absence  of  such  definite  basis  it  is  sufficient  for  all  practical 
purposes  to  take  it  at  the  center  of  the  float  radially,  though  its 
true  location  would  lie  somewhat  outside  this  point.  Counting 
the  circumference  through  this  point  as  the  pitch,  the  actual  dis- 
tance traveled  by  the  boat  per  revolution  is  less  by  the  amount  of 
the  slip,  which  is  usually  found  from  15  to  25  or  30  per  cent. 

The  circle  whose  circumference  is  equal  to  the  distance  trav- 
eled per  revolution  is  sometimes  known  as  the  rolling  circle.  It 
is  so  called  from  the  fact  that  the  speed  of  the  boat  is  the  same  as 
though  it  were  carried  on  wheels  of  this  diameter,  "which  rolled  on 
a  supporting  surface  as  wagon  wheels  along  a  smooth,  level  road. 
The  solutions  of  problems  relating  to  the  revolutions,  diam- 
eter and  slip  of  paddle  wheels  are  found  in  the  same  general  man- 
ner as  for  the  screw  propeller,  and  the  re-suiting  equations  are 
similar  to  those  found  in  Sec.  80  [i],  with  the  substitution  for  p 
of  D,  as  defined  below,  and  88  for  101.3. 

Let  D  =  diameter  of  rolling  or  pitch  circle.  i 

N  =  revolutions  per  minute. 

u  =  speed  in  miles  per  hour. 

^  i=  slip  ratio. 

Then,  as  with  the  screw  propeller,  we  have  : 
DN  -  88  u 


88  u 
D    - 


These  may  be  illustrated  by  the  following  examples  : 

(i)  Given  diameter  of  rolling  circle,  36  feet;  revolutions,  45 
per  minute  ;  speed,  14  miles  per  hour.    Find  the  slip  ratio. 
Operation  : 

D  N  =  36  X  45  =  1620 

88  u  —  88  X  H  =  1232 

1620  —  1232  -i-  1620  =  388  -r-  1620  =  23.3  per  cent. 


534  PRACTICAL  MARINE  ENGINEERING. 

(2)  Given  diameter  of  rolling  circle,  30  feet ;  revolutions,  50 
per  minute,  what  speed  can  be  made,,  allowing  a  slip  of  30  per 
cent? 

Operation : 

D  N  =  30  X  50  =  J5oo 

i  —  s  =  i  —  .30  =  .70 

.70  X  1500=  1050 

1050  -r-  88  =  11.9  miles  per  hour  =  10.35  knots. 

(3)  Given  a  speed  of  18  miles  per  hour,  a  slip  of  24  per  cent, 
and  a  wheel  whose  rolling  circle  has  a  diameter  of  40  feet.    Re- 
quired the  number  of  revolutions  per  minute. 

Operation : 

88  X  «  =  88  X  18  =  1604 

i  —  ^  =  i  —  .24  =  .76 

D  (i  —  s)  =  40  X  76  =  304 

1604  -T-  30.4  =  52.8  revolutions  per  minute. 

(4)  Given  a  speed  of  14  miles  per  hour ;  revolutions,  40  per 
minute ;  slip,  28  per  cent.     Find  the  corresponding  diameter  of 
rolling  circle. 

Operation : 

88  X  «  =  88  X  14  =  1232 
i  —  s=  i  —  .28  =  .72 
N  (i  —  s)  —  40  X  -72  =  28.8 
1232  —  28.8  =  42.8  feet. 

Sec.  82.  POWERING  SHIPS. 

The  subject  of  the  powrering  of  ships  is  one  which  can  be  here 
only  referred  to  in  a  brief  and  elementary  way.  The  usual  prob- 
lems are  to  find  the  power  required  to  drive  a  given  ship  at  a  pro- 
posed speed,  or  the  probable  speed  for  a  given  ship  with  a  given 
power.  Such  problems  require  a  knowledge  of  the  relation  be- 
tween power,  speed  and  the  ship.  In  the  present  state  of  our  in- 
formation on  this  subject,  such  relation  cannot  be  accurately  ex- 
pressed by  any  ordinary  formula  or  equation.  Several  approxi- 
mate formulae  have,  however,  been  employed  for  the  solution  of 
such  problems,  and  among  them  none  has  perhaps  been  of  wider 
general  usefulness  than  the  so-called  Admiralty  coefficient 
formula. 

Let/f=     I.H.P. 

D  =     displacement  in  tons. 

v  =     speed  in  knots. 

K  =     a  coefficient. 


PROPULSION  AND  POWERING.  535 

Then  according  to  this  formula  we  have : 

H  —  -      * 

and  solving  for  speed  : 
3  /~HK~ 

and  solving  for  the  coefficient : 

K  =  j^_ 

The  whole  point  in  the  use  of  the  formula  is  to  properly  se- 
lect the  values  of  the  coefficient  K  in  accordance  with  the  special 
features  of  the  case,  including  the  form  and  size  of  the  ship,  pro- 
posed speed,  probable  efficiency  of  propulsion,  etc.  The  safest 
plan  is  to  find  values  of  K  from  the  trial  data  of  actual  ships  of 
about  the  same  size,  character  of  form  and  speed,  as  the  pro- 
posed case,  and  to  be  guided  by  such  values  in  the  selection  of 
the  coefficient  for  the  proposed  case.  There  are  other  special 
methods  for  obtaining  from  the  trial  data  of  ships  of  similar 
form,  by  the  so-called  law  of  comparison,  the  suitable  values  for 
a  proposed  case,  even  when  the  sizes  and  speeds  differ  consider- 
ably from  those  of  the  proposed  case.  Into  the  details  of  these 
points,  however,  we  cannot  here  enter.  Some  general  sugges- 
tions regarding  the  value  of  K  with  a  few  illustrative  examples 
must  suffice. 

We  find  then  by  experience  that  in  general  the  value  of  K 
is  greater  (and  hence  the  I.H.P.  relatively  less)  as  the  ship  is 
larger,  but  more  especially  as  she  is  longer,  also  as  she  is  nar- 
rower in  proportion  of  length  to  beam,  and  as  she  is  finer  in 
form,  especially  in  the  water  lines. 

In  the  reverse  cases  the  values  of  K  will  be  smaller,  and  the 
I.H.P.  relatively  larger.  The  values  of  K  are  also  smaller  and 
the  I.H.P.  relatively  larger  as  the  speed  is  higher  in  proportion 
to  the  length,  or,  more  exactly,  as  the  speed  is  higher  in  propor- 
tion to  the  square  root  of  the  length.  For  small  launches  and 
such  craft  driven  at  speeds  in  miles  or  knots  greater  than  ;/Z  in 
feet,  the  values  of  K  will  be  quite  small,  ranging  perhaps  from 
100  to  150.  At  lower  speeds  equal  to  or  less  than  t/Z" the  values 
will  rise  to  perhaps  200  and  more  with  fine  form  and^small  pro- 
portion of  beam  to  length.  For  yachts  and  craft  of  similar  form, 
moderately  fine  and  at  fairly  high  speeds,  values  of  200  above 


536  PRACTICAL  MARINE  ENGINEERING. 

and  below  will  be  found.  For  torpedo  boats,  with  their  narrow 
proportions  and  fine  form,  their  excessive  speeds  carry  them  into 
a  set  of  conditions  where  the  coefficients  are  larger  and  the 
power  required  relatively  less  than  we  might  expect.  Varying 
with  size  and  other  conditions,  values  of  200  above  and  below 
are  found  for  boats  of  this  character.  For  mercantile  vessels  of 
moderate  size,  rather  full  form  and  moderate  speed,  the  values 
will  be  usually  found  from  perhaps  220  to  250.  For  larger  mer- 
cantile vessels  at  moderate  speeds  or  for  those  of  moderate  size 
under  exceptionally  good  conditions  the  values  may  rise  from 
250  to  300.  For  fast  passenger  boats  varying  with  size,  and 
other  conditions,  values  from  220  to  280  may  be  expected.  For 
naval  vessels,  cruisers  and  battleships,  from  200  to  250  is  the 
usual  range. 

These  various  values  are  not  intended  as  marking  definite 
limits,  nor  can  they  enable  a  person  without  individual  judgment 
to  properly  select  a  suitable  value  for  a  given  case.  They  are 
intended  simply  as  general  suggestions  of  the  range  of  values 
commonly  met  with. 

We  will  now  solve  a  few  examples  to  illustrate  the  use  of 
this  formula. 

We  may  first  note  that  D\  means  the  cube  root  of  the 
square,  or  the  square  of  the  cube  root  of  the  displacement  in 
tons,  and  hence  with  a  table  of  squares  and  cubes  or  square  and 
cube  roots,  the  value  desired  may  be  readily  found.  In  some 
hand  books  values  of  />§  are  given  directly. 

(i)  Given  D  =  3200,27  =12  and  take  K  =  230.  Required 
the  power. 

From  arable  of  squares  we  have  (32)*=  1024,  and  hence 
(320o)2  =  10,240,000.  Looking  in  the  column  of  cubes  of  num- 
bers of  three  figures  we  find  that  the  nearest  cube  is  10,218,313, 
and  that  the  number  corresponding  is  217.  This  will  be  suffi- 
ciently near  for  all  practical  purposes,  and  is  therefore  taken  as 
the  value  of  D\.  We  have  also  (12)'  =  1728.  Hence  we  have  : 

=   1630  Ans. 


230 


(2)  Given  a  yacht  of  displacement  366  tons,  to  be  driven  at 
a  speed  of  18  knots.  Assume  k  =  200  and  find  the  necessary 
power.  In  this  case  (366)'  =  133,956  and  the  number  corre- 
sponding to  the  nearest  cube  is  51.2.  Also  (i8)3  =  5832.  Hence 


PROPULSION  AND  POWERING.  537 

H  =  5I'2  X  5832  =   1493. 

200 

(3)  Given  D  =  7243,  v  —  16  and  take  K  —  240.  Find  the 
power.  Without  important  error  we  may  drop  the  last  3  tons  so 
as  to  bring  the  number  within  the  range  of  the  usual  tables  of 
squares  and  cubes.  We  have  then  (724)2  =  524,176,  and  hence 
(7240)2  =  52,417,600.  The  number  corresponding  to  the  nearest 
cube  is  374.  Also  (i6)3  =  4096.  Hence  : 


H  = 


374  X  4°96 


240 

(4)  What  speed  may  be  expected  from  a  liner  of  15,400  tons 
displacement  and  26,000  I.H.P.?  Take,  in  this  case,  ^  =  250. 
Then  (i54)2  =  23716  and  hence  (  1  5400)'  =  237,160,000.  The 
number  corresponding  to  the  nearest  cube  is  619.  Then  we  have 


s  /  26,000  x  25° 


~-  V          619          :  F  10,500  =  21.9. 

(5)  Given  D  =  8320,  v  =  13  and  H  =  3400.  Required  the 
value  of  K. 

We  have  (832)'=  692,224  and  hence  (8320)'  =  69,222,400. 
The  number  corresponding  to  the  nearest  cube  is  411.  Also 


= 


Hence  we  have  : 

K    =    411     X     2197 

3400 


Sec.  83.  REDUCTION  OF  POWER  WHEN  TOWING  OR 
WHEN  VESSEL  IS  FAST  TO  A  DOCK. 

It  is  well  known  that  the  power  developed  by  the  engine 
when  the  ship  is  towing  is  less  than  when  she  is  running  free,  the 
steam  pressure  and  cut-off  being  the  same  ;  also  that  at  a  dock 
trial  (engines  running,  but  ship  fast  to  the  dock)  the  power  is 
considerably  less  than  may  be  developed  in  free  route  under  the 
same  steam  pressure  and  point  of  cut-off. 

To  explain  these  results  let  us  first  assume  that  the  ship, 
boilers,  engine  and  propeller  are  all  properly  designed  for  a 
given  speed.  This  means  that  with  a  given  boiler  pressure  (say 
180  Ibs.)  the  boilers  will  be  able  to  supply  steam  enough  to  drive 
the  engines  at  the  designed  revolutions  (say  ioo)  and  thus  de- 
velop the  designed  power,  while  the  propeller  with  a  certain  slip 
(say  20  per  cent)  will  drive  the  ship  at  the  designed  speed  (say  16 
knots).  Now  it  must  first  be  noted  that  all  of  these  conditions 


538 


PRACTICAL  MARINE  ENGINEERING. 


go  together,  and  if  any  one  of  them  is  disturbed  it  will  react  on 
all  the  others.  The  next  point  is  that  a  constant  set  of  pressures 
throughout  the  engine  means  a  constant  reduced  mean  effective 
pressure,  a  constant  turning  moment  on  the  shaft  and  a  nearly 
constant  thrust,  and  hence  a  nearly  constant  resistance  over- 
come. Now  at  the  regular  speed,  if  the  resistance  is  increased, 
as  by  taking  up  a  tow,  what  will  be  the  immediate  result?  Evi- 
dently the  speed  will  decrease  until  at  some  reduced  speed  the 
nearly  constant  thrust  will  balance  the  resistance,  and  the  mo- 
tion will  become  uniform  again.  The  greater  the  increase  in  re- 
sistance at  the  regular  speed — that  is,  the  larger  the  tow — the 
lower  the  speed  at  which  the  nearly  constant  thrust  will  be  able 
to  balance  the  resistance  and  thus  produce  steady  conditions. 


19 

•15 

13 
12 
11 

CO 

fE  8 

UJ      ' 
LU 

C-    6 

co 

1 
3 
2 

( 

I/ 

l/ 

/ 

/ 

\  / 

/ 

7_ 

1             i 

i 

I 

I 

j 

/ 

)            10           30           30           40           5'J           JO           ',o           80           90          iO 
REVOLUTIONS 

Fig.   294.     Diagram   Showing  Relation   Between  Revolutions  and 
Speed  for  Constant  Turning  Moment. 

The  whole  question  as  regards  power  developed  now  turns 
on  the  revolutions  at  this  reduced  speed.  In  other  words,  how 
do  revolutions  and  speed  vary  for  a  constant  turning  moment, 
and  a  nearly  constant  thrust  developed  or  resistance  overcome? 
This  is  best  answered  by  experimental  data,  which  give  us  a  re- 
lation similar  to  that  shown  in  Fig.  294.  Revolutions  are  laid 
off  horizontally  and  speed  vertically.  If  we  suppose  that  90 
revolutions  and  14  knots  are  the  designed  conditions,  as  indi- 
cated on  the  curve,  then  the  diagram  shows  how  the  revolutions 
and  speed  vary  for  a  constant  thrust.  In  particular  the  curve 
shows,  as  the  tow  is  increased  in  amount  and  the  speed  for  a 


PROPULSION  AND  POWERING.  539 

given  thrust  decreases  more  and  more,  so  likewise  do  the  revolu- 
tions decrease,  though  at  a  slower  rate.  Hence  with  the  de- 
crease of  speed  the  slip  constantly  increases.  The  relations  as 
shown  by  this  curve  furnish  the  key  for  the  solution  of  all  ques- 
tions regarding  the  variation  of  the  power.  The  work  done  by 
the  engine  is  a  product  of  the  revolutions  into  other  factors,  and 
since  these  other  factors  include  merely  dimensions  of  the  engine 
and  mean  effective  pressure,  and  since  by  assumption  all  of  these 
remain  constant,  it  is  evident  that  under  the  conditions  assumed 
the  power  developed  will  vary  directly  with  the  revolutions. 
Hence  the  diagram  shows  the  relative  decrease  of  power  with  de- 
creasing speed,  as  well  as  the  actual  decrease  in  revolutions. 

If  we  should  continue  to  add  to  the  tow  indefinitely  we 
should  at  length  reach  a  condition  similar  to  that  of  a  vessel  tied 
to  a  dock ;  that  is,  a  condition  where  the  speed  has  become  re- 
duced to  nothing  and  the  revolutions  reduced  in  quite  marked 
degree.  The  exact  relation  between  revolutions  in  free  route 
and  when  fast  to  a  dock  will  of  course  depend  on  the  special  cir- 
cumstances. The  mean  effective  pressure  remains  the  same, 
however,  and  the  work  done  and  power  developed  will  therefore 
vary  simply  with  the  revolutions  according  to  a  law  similar  to 
that  shown  in  the  figure. 

To  sum  up  the  matter,  therefore,  the  power  falls  off  because 
the  revolutions  fall  off,  and  the  revolutions  fall  off  because  the 
speed  falls  off,  and  because  at  the  reduced  speed  and  increased 
slip  the  constant  turning  moment  of  the  engine  can  no  longer 
turn  the  propeller  at  the  original. number  of  revolutions. 

The  reason  why  of  the  facts  expressed  by  the  curve  in  Fig. 
294,  on  which  the  whole  matter  turns,  is  to  be  found  in  the  funda- 
mental relation  between  revolutions,  slip,  thrust,  etc.,  a  complete 
discussion  of  which  is  of  course  beyond  our  present  purpose. 
Once  these  relations  accepted  as  experimental  truth,  however, 
the  desired  explanation  is  seen  to  flow  from  them  as  a  necessary 
consequence. 

Sec.  84.  TRIAI,  TRIPS. 

The  general  purpose  of  a  trial  is  to  determine  the  power  or 
speed  which  may  be  maintained  for  a  certain  distance  or  time. 
In  addition  to  these  fundamental  purposes,  information  relating 
to  the  general  problem  of  resistance  and  propulsion  may  also  be 
gained,  as  well  as  that  bearing  on  other  points  which  may  be  the 
object  of  special  inquiry.  We  shall  not  here  refer  especially  to 


540  PRACTICAL  MARINE  ENGINEERING. 

the  determination  of  power,  as  that  has  been  already  sufficiently 
treated  in  Sec.  55  [3], 

For  the  determination  of  speed  alone  it  is  sufficient  to  ob- 
tain observations  of  distance  and  time.  The  revolutions  should, 
however,  be  also  taken,  in  order  that  the  slip  of  the  propeller 
may  be  found.  For  speed  trials  we  may  use  a  long  course,  as, 
for  example,  from  20  to  100  miles  or  more,  over  which  but  one 
run,  or,  more  commonly,  one  run  in  each  direction  is  made ;  or, 
on  the  other  hand,  a  short  course  of  I  or  2  miles,  over  which  as 
many  runs  may  be  made  as  desired. 

For  marking  off  the  course,  buoys  or  ships  at  anchor  are  often 
used  for  the  long  course,  while  range  marks  on  shore  for  the 
limits  and  buoys  for  the  direction  and  location  are  commonly 
employed  for  the  short  course.  At  each  end  of  the  short  course 
there  should  be  plenty  of  room  for  making  turns  and  gathering 
headway  before  entering  the  course  for  the  return  run.  The  free 
space  available  for  this  purpose  should  be  not  less  than  from 
one-half  to  one  mile. 

To  eliminate  the  error  due  to  the  tide  on  the  long  course 
run,  tidal  observations  should  be  made  from  vessels  anchored 
along  the  course  by  means  of  a  patent  log  or  equivalent  device, 
and  from  the  results  the  average  tidal  influence  may  be  deter- 
mined. To  eliminate  the  tidal  error  on  short  course  trials  the 
runs  are  made  in  both  directions  and  an  average  is  taken.  This 
may  be  either  a  simple  average  or  the  result  of  a  "continued 
average,"  as  illustrated  below. 

Suppose  four  runs  made,  two  in  each  direction,  and  let  the 
resulting  speeds  in  order  be  those  entered  in  the  column  on  the 
left. 

North     17.2     . 

17.00 

South     16.8  17-075 

17.15  17.10 

North     17.5  I7-I25 

17.10 

South     16.7 

An  average  is  first  made  of  Nos.  i  and  2,  then  of  2  and  3, 
and  then  of  3  and  4,  and  these  are  put  in  the  second  column. 
Then  these  are  averaged  in  like  manner  and  put  in  the  third 
column,  and  these  are  again  averaged  for  the  final  result,  which, 
in  the  above  case,  is  17.10.  With  six  runs  the  operation  is  car- 


PROPULSION  AND  POWERING.  541 

ried  out  in  the  same  way.  While  this  is  often  considered  as  the 
only  correct  way  of  averaging  such  a  series  of  runs,  it  may  be 
shown  that  such  is  by  no  means  the  case,  and,  as  a  matter  of  fact, 
that  under  ordinary  conditions  the  simple  average  .will  give  quite 
as  probable  a  result  as  the  more  complex  method.  In  the  above 
case  the  simple  average  would  give  17.05,  as  against  17.10,  a 
difference  of  .05  knot,  and  the  former  value  is  quite  as  likely  to 
be  correct  as  the  latter. 

In  some  cases  it  is  desirable  to  make  a  complete  speed  trial 


riU 

18 
1G 
14 

6 

z  12 
x. 

z 

Q 

u)  10 
m 

CL 
CO 

8 
0 
4 
2 

( 

./ 

/ 

/ 

/ 

f 

/ 

/ 

j 

/ 

/ 

/ 

/ 

)           10          20          30          40          50          60          70          80          90         10 

R  EVOLUTIONS                                         ^»"««  £nuin**ring 

Fig.  295.    Diagram  of  Revolutions  and  Speed. 

and  thus  obtain  a  series  of  values  of  the  power,  revolutions  and 
speed  from  full  power  conditions  down.  This  may  be  done  on 
the  measured  mile  or  short  course  by  making  runs  in  pairs,  the 
conditions  for  each  pair  remaining  as  nearly  constant  as  possible, 
while  from  one  pair  to  another  the  conditions  change  over  the 
complete  range  to  be  included  in  the  trial.  The  average  results 
in  speed,  power  and  revolutions  are  then  used  for  plotting  the 
curves  showing  the  various  relations  desired.  Such  a  curve 
showing  the  relation  between  revolutions  and  power  is  shown  in 


542 


PRACTICAL  MARINE  ENGINEERING. 


Fig.  296,  together  with  the  spots  which  may  represent  the  actual 
single  observations.  The  curve  may  then  be  drawn  through 
and  among  the  spots  as  a  method  of  getting  a  graphical  average ; 
or  otherwise  the  values  may  be  averaged  numerically  and  plotted 
as  a  series  of  averages,  and  the  curve  then  drawn  through  them. 
As  a  somewhat  shorter  method,  a  series  of  runs  may  be 
taken  in  each  direction,  beginning  at  the  highest,  and  at  con- 
stantly decreasing  revolutions.,  The  results  for  speed  and  revo- 
lutions are  then  plotted,  as  shown  in  Fig.  295,  and  a  fair  curve 
drawn  through  and  among  the  spots.  This  is  then  taken  as  the 


1000 


0          -10          20          30          40  50  60  70  80  90 

REVOLUTIONS  Marine  JJnui>, 

Fig.  296.    Diagram  of  Revolutions  and  Horse  Power. 

relation  between  revolutions  and  speed.  The  relation  between 
revolutions  and  power  is  also  plotted,  as  in  Fig.  296.  Then,  by 
the  aid  of  these  two,  the  speed-power  curve  may  be  plotted,  as 
shown  in  Fig.  297.  We  will  now  note  briefly  the  computations 
arising  in  connection  with  such  trials.  The  observations  with 
which  we  are  here  concerned  are  simply  time  and  revolutions. 

Let  the  course  be  a  measured  mile  (marine  or  statute,  as  the 
case  may  be),  and  let  the  time  on  the  course  be  t,  expressed  in 
minutes  and  decimals.  This  is  usually  determined  by  a  stop- 
watch reading  the  half  or  quarter  second.  The  value  cannot, 


PROPULSION  AND  POWERING. 


543 


however,  be  depended  on  as  accurate  to  much  within  i  second. 
Then  if  v  denotes  the  speed  we  have : 

v  =  60  -f-  t 

The  revolutions  will  be  obtained  from  the  counter  by  sub- 
tracting the  readings  at  the  entrance  and  end  of  the  course.  This 
will  give  the  number  of  revolutions  for  the  course.  Let  this  be 
denoted  by  R.  Then 

r>       % 

Revolutions  per  minute  =  — 


9000 
SOOO 

roa 
coco 


X'5000 


4000 


3000 


2000 


1000 


16    18    20 

Marint  Snginttnng 


Diagram  of  Speed  and  Horse  Power. 


Also  let  p  =  pitch  of  propeller. 

Then  assuming  the  course  to  be  a  nautical  mile,  we  have  : 

(pR  -6080)  =  slip  In  feet,  and  pR  ~  6o8°  =  slip  ratio. 

pR 

These  computations  may  be  illustrated  by  the  following  ex- 
ample : 

Let  the  course  be  a  mile  of  6,080  feet,  and  let  the  following 
data  be  taken  : 

Counter  at  entrance.  Counter  at  end.  Time. 

Run  north     106,248  106,654  4  m.  26  sec. 

Run   south     107,112  107,542  4m.  33  sec. 

Pitch  of  propeller  18  feet. 


544  PRACTICAL  MARINE  ENGINEERING. 

Required  the  mean  speed  and  slip  for  the  two  runs. 

For  the  run  north  the  revolutions  are  106,654 — 106,- 
248  =  406. 

For  the  run  south  the  revolutions  similarly  found  are  430. 
The  average  revolutions  are  then  418.  The  speed  north  is 
60  -T-  4.433  =  13-53-  The  speed  south  is  60  -r-  4.55  =  13.19.  The 
mean  speed  is  then  13.36. 

The  slip  in  feet  =  418  X  18  —  6080  —  7524  — 6080  =  1444. 

The  slip  ratio  =         4   =  19.2  per  cent. 

7524 

Sec.  85.   SPECIAL  CONDITIONS  FOR  SPEED  TRIADS. 

In  speed  or  power  trials  the  purpose  is  often  the  develop- 
ment of  the  maximum  speed  or  power,  and  in  the  present  section 
we  may  note  the  more  important  points  connected  with  the  ful- 
filment of  these  purposes. 

Boilers.  Where  there  is  a  record  performance  to  be  made 
there  must  be  no  loss  of  evaporative  efficiency  due  to  accumula- 
tions of  soot  and  ashes  on  the  fire  side,  or  of  oil,  scale  or  mud  on 
the  water  side.  Hence  especial  care  must  be  taken  to  see  that 
the  boilers  are  thoroughly  clean  on  both  fire  and  water  sides. 

Fuel.  If  possible,  the  fuel  should  be  of  the  highest  grade 
and  carefully  selected  with  reference  to  clean,  free  burning 
qualities. 

Engines.  The  engines  should  be  adjusted  with  the  various 
joints  sufficiently  loose  to  avoid  danger  from  heating,  and  at  the 
same  time  not  sufficiently  loose  to  hammer  seriously.  Special 
attention  must  be  paid  to  oiling  gear,  and  also  to  the  provision 
for  supplying  water  in  case  the  bearings  tend  to  become  hot. 

Ship.  The  ship  should  be  lightened  as  much  as  possible — 
that  is,  the  displacement  should  be  made  as  small  as  possible. 
This  point  must  not  be  carried  so  far,  however,  as  to  decrease 
the  draft  or  change  the  trim  sufficiently  to  bring  the  tips  of  the 
propeller  blades  too  near  the  surface  of  the  water.  In  the  latter 
case  the  propeller  will  fail  to  develop  the  necessary  thrust  and 
the  highest  speed  cannot  be  attained.  The  bottom  of  the  ship 
should  also  be  thoroughly  clean  and  fresh  painted,  or,  if  cop- 
pered, clean  and  polished,  if  not  too  large.  The  propeller  should 
also  be  looked  after,  and  if  there  is  opportunity  it  should  be 
cleaned  and  the  edges  sharpened. 


REFRIGERATION.  545 


CHAPTER    XI. 

REFRIGERATION. 

Sec.  86.  GEKERAI,  PRINCIPLES. 

In  connection  with  the  general  principles  of  refrigeration 
reference  should  be  made  to  Section  57,  where  the  general  nature 
of  heat  and  its  relation  to  matter  is  discussed.  The  fundamental 
problem  of  refrigeration  is  the  abstraction  of  heat  from  some 
body  or  substance  A,  or  the  maintenance  of  such  substance  A  at 
a  temperature  lower  than  that  of  the  surrounding  air.  This  is 
most  conveniently  brought  about  by  bringing  the  substance  A 
into  relation  with  another  cooling  substance  B  at  a  lower  tem- 
perature, such  that  heat  may  readily  pass  by  conduction  from 
one  to  the  other.  The  heat  then  flows  from  A  to  B,  and  thus  the 
end  desired  is  brought  about.  It  is  clear,  however,  that  unless 
there  is  a  continuous  renewal  of  the  substance  B,  or  some  way  of 
removing  the  heat  which  flows  into  it,  then  in  the  end  the  two 
substances  A  and  B  will  come  to  the  same  temperature,  and  if 
this  is  lower  than  that  of  the  surroundings,  it  will  gradually  rise 
until  both  A  and  B  are  in  equilibrium  with  their  general  sur- 
roundings. Again  it  is  seen  that  if  the  substance  A  is  kept  below 
the  temperature  of  its  surroundings  there  will  be  a  constant  flow 
of  heat  from  these  surroundings  (structural  material,  earth,  air, 
water,  etc.)  into  it,  and  this  heat  must  be  as  constantly  removed 
by  conduction  into  the  substance  B  at  still  lower  temperature, 
which  again  must  be  renewed  in  order  to  maintain  its  capacity 
for  absorbing  heat  from  A.  Again  we  may  have  two  different 
cases,  according  as  the  substance  A  is  cooled  by  the  conduction 
of  its  heat  directly  into  B,  or  first  into  some  intermediate  sub- 
stance such  as  air  and  then  into  B.  In  other  \Vords,  the  sub- 


546  PRACTICAL  MARINE  ENGINEERING. 

stance  B  may  affect  A  directly,  or  through  the  intermediate  ac- 
tion of  the  air  surrounding  both  of  them. 

Thus  in  making  artificial  ice  the  water  to  be  frozen  is 
brought  as  directly  as  possible  under  the  influence  of  the  cooling 
substance,  whatever  it  may  be,  while  in  certain  systems  for  the 
refrigeration  of  meat,  etc.,  in  a  refrigeration  or  cold  storage 
room,  the  meat  is  kept  cool  by  the  action  of  the  cold  air  of  the 
room,  which,  in  turn,  is  cooled  by  the  action  of  the  cooling  sub- 
stance, usually  conducted  through  coils  of  pipe  about  the  walls 
of  the  room.  In  other  systems  of  refrigeration  or  cold  storage, 
air  itself  is  made  the  cooling  substance,  and  the  cooled  air  is 
passed  through  the  storage  room,  thus  acting  directly  upon  the 
substances  stored  therein. 

With  the  foregoing  by  way  of  a  statement  of  general  prin- 
ciples we  come  now  to  the  production  of  the  cooling  substance. 
In  other  words,  how  shall  we  find  or  produce  a  substance  whose 
temperature  is  far  below  the  usual  temperature  of  the  air,  and 
which  may  be  made  available  for  the  purposes  outlined  above? 
To  this  end  we  have  two  general  methods ;  one  involving  a 
change  of  state,  either  physical  or  chemical  or  both,  and  the 
other  the  compression,  cooling  and  expansion  of  an  elastic  gas 
such  as  air.  Illustrations  of  these  methods  will  be  found  in  the 
systems  of  refrigeration  described  in  the  following  sections. 

Sec.  87.  REFRIGERATION  BY  FREEZING  MIXTURES. 

If  salt  and  ice  are  mixed  there  is  a  tendency  for  the  mixture 
to  pass  into  the  liquid  state.  As  to  just  why  this  is  so  we  are 
not  concerned,  but  simply  with  the  fact.  In  answer  to  this  ten- 
dency the  two  substances  pass  rapidly  from  the  solid  into  the 
liquid  state,  thus  forming  a  brine,  or,  more  exactly,  the  ice 
passes  from  the  solid  to  the  liquid  state  and  the  salt  dissolves  in 
the  liquid.  Now  ice  cannot  pass  from  a  solid  to  a  liquid  state 
without  absorbing  heat.  This  point  has  been  referred  to  in  Sec. 
57  t1]*  where  it  was  also  noted  that  the  term  latent  heat  is  ap- 
plied to  the  heat  which  is  thus  involved  in  a  change  of  physical 
state.  Heat  must  therefore  be  supplied  from  somewhere  in  or- 
der that  the  change  from  ice  to  liquid  may  take  place.  Further- 
more, due  to  the  physical  and  chemical  forces  at  work,  this 
change  takes  place  faster  than  heat  can  be  supplied  from  the 
general  surroundings,  and  since  it  must  come  from  somewhere 
it  is  drawn  from  the  substances  themselves,  brine,  salt  and  ice, 


RRFRJGERA  TION.  547 

which  are  thus  reduced  to  a  much  lower  temperature  than  they 
would  have  if  separate.  Thus  a  mixture  of  ice  and  salt  forms  a 
brine  having  a  temperature  of  about  —  5  Fah.,or  about  37°  below 
the  freezing  point  of  ice.  Such  solutions  or  mixtures  are  known 
as  freezing  mixtures,  and  the  brine  thus  formed  may  then  be 
used  as  a  cooling  or  freezing  agent  in  whatever  way  may  be  most 
convenient. 

Thus  in  the  ordinary  manner  of  freezing  ice-cream  and  ices 
the  ice-salt  mixture  is  commonly  used,  inclosed  in  a  casing 
which  surrounds  an  inner  vessel  containing  the  substance  to  be 
frozen.  In  the  manner  above  described  then  the  ice  will  be 
melted,  a  brine  will  be  formed,  and  heat  will  be  withdrawn  first 
from  the  freezing  mixture  itself,  and  then  from  the  substance  in 
the  inner  vessel,  which  thus  becomes  cooled  down  to  its  freezing 
point.  Next  its  own  latent  heat  will  be  drawn  upon,  and  thus 
finally  the  substance  becomes  frozen  as  desired. 

There  are  many  such  mixtures  composed  of  various  chemi- 
cals, and  by  means  of  which  temperatures  from  o  to  —  50  Fah. 
may  be  obtained.  For  the  general  purpose  of  refrigeration,  how- 
ever, the  use  of  such  mixtures  has  not  been  found  as  efficient  as 
other  means,  and  it  will  not  be  necessary  therefore  to  further 
refer  to  them  in  the  present  connection. 

Sec.  88.   REFRIGERATION  BY  VAPORISATION  AND 
EXPANSION. 

We  will  next  consider  the  application  of  substances  like 
ammonia  or  carbonic  acid,  which  are  gaseous  at  the  usual  tem- 
peratures, but  may  be  liquified  at  low  temperatures  and  under 
suitable  pressures.  Anhydrous  ammonia  (ammonia  without 
water)  has  a  boiling  point  under  atmospheric  pressure  of  37°  be- 
low zero.  With  higher  pressures  the  boiling  point  rises.  As  we 
have  already  seen  in  Sec.  57,  a  liquid  passing  into  the  state  of 
vapor  absorbs  a  certain  amount  of  heat,  and  this  latent  heat,  as 
it  is  termed,  will  be  drawn  either  from  the  surroundings  or  from 
'the  liquid  itself,  or  from  both,  thus  lowering  their  temperatures. 
In  order  to  utilize  these  properties  of  ammonia  the  refrigerating 
apparatus  consists  of  the  following : 

(i)  A  series  of  expansion  evaporating  coils  which  are  placed 
in  the  refrigerator  room  or  space  to  be  cooled,  or  which  in  other 
systems  are  surrounded  by  a  liquid  which  is  used  as  the  imme- 
diate cooling  agent  in  the  coils  of  the  refrigerator  room. 


548  PRACTICAL  MARINE  ENGINEERING. 

(2)  A  reservoir  containing  liquid  ammonia  which  is  allowed 
to  flow  as  may  be  required  into  the  expansion  coils. 

(3)  A  pump  which  withdraws  the  vapor  from  the  expansion 
coils  and  then  compresses  it  back  into  the  coils  of  a  condenser, 
which  are  surrounded  by  cool  water.    Here,  under  the  influence 
of  the  pressure  and  moderate  temperature,  the  vapor  becomes 
condensed  to  liquid  and  then  flows  to  the  reservoir  from  which 
it  started.    The  two  fundamental  parts  of  the  process  are  there- 
fore (i)  evaporation  and  expansion,  (2)  compression  and  con- 
densation.   In  this  manner  the  continuous  operation  of  the  pump 
insures  the  formation  and  continuous  flow  of  ammonia  vapor  at 
low  temperature  through  the  cooling  coils.    The  vapor  is  thus  in 
condition  to  absorb  heat  through  the  metal  of  the  coils  from  the 
surroundings,  either  air  or  liquid,  and  thus  the  refrigeration  is 
effected.    Where  a  liquid  is  employed  as  the  immediate  cooling 
agent  it  is  usually  a  brine  made  with  common  salt,  which,  after 
having  been  cooled  down  by  giving  up  its  heat  to  enable  the 
ammonia   to   evaporate,   is   then,  circulated  by   a   brine   pump 
through  the  coils  of  the  refrigeration  room. 

It  has  been  well  said  that  the  action  of  the  ammonia  in  this 
round  of  operations  is  like  a  sponge.  It  vaporizes  and  expands 
in  the  expansion  coils  and  absorbs  or  soaks  in  the  heat  from  its 
surroundings.  Then  it  is  compressed  and  the  heat  is  forced  or 
"squeezed"  out,  and  it  is  ready  for  a  new  round,  thus  acting  as 
a  carrier  of  heat  away  from  the  substance  to  be  cooled. 

It  may  aid  further  in  understanding  the  action  of  the  liquid 
ammonia  in  the  refrigerating  coils  to  note  that  relative  to  the  air 
or  brine  surrounding  these  coils  the  ammonia  is  situated  some- 
what like  the  water  in  a  water-tube  boiler  with  hot  gas  on  the 
fire  side  of  the  tubes.  The  furnace  gases  are  hot  relative  to  the 
water,  and  so  heat  tends  to  flow  through  the  tubes  into  the 
water,  thus  forming  steam.  So  is  the  temperature  of  the  air  or 
brine  about  the  coils  far  above  that  at  which  ammonia  would 
naturally  exist  in  the  liquid  form  under  the  pressure  in  the  coils. 
In  fact,  the  liquid  ammonia  when  first  admitted  is  itself  far  above 
this  temperature,  so  that  the  first  result  is  a  tendency  for  the 
liquid  to  fly  into  vapor  immediately,  drawing  on  its  own  sensible 
heat  to  supply  the  necessary  latent  heat,  and  thus  cooling  the  re- 
maining liquid  and  the  vapor  formed.  Then  the  heat  from  the 
surrounding  air  or  brine  flows  in  and  thus  the  vaporization  is 
completed.  We  may  thus  say  that  the  liquid  ammonia  is  boiled 


REFR1GERA  TION.  549 

into  vapor  chiefly  by  the  heat  which  it  draws  from  the  surround- 
ing air  or  brine.  So  likewise  if  we  should  set  a  jar  of  liquid  am- 
monia into  a  snow  bank,  the  latter  would  be  warm  relative  to  the 
boiling  point  of  the  ammonia  under  atmospheric  pressure,  and 
in  consequence  the  snow  would  play  the  part  of  the  fire  in  the 
usual  case  with  water  and  supply  the  heat  which  would  serve  to 
vaporize  the  ammonia,  the  snow  becoming  thereby  cooled  by 
reason  of  its  loss  of  heat. 

Having  thus  sketched  the  general  outline  of  the  process, 
the  following  additional  points  may  be  mentioned : 

The  liquid  ammonia  is  usually  under  a  pressure  of  125-175 
Ibs.  per  square  inch,  corresponding  to  temperatures  from  about 
70  to  90  degrees.  By  the  action  of  the  ammonia  pump,  which 
draws  the  vapor  from  the  refrigerating  coils,  the  pressure  in  the 
latter  is  maintained  at  from  30  to  60  Ibs.,  corresponding  to  tem- 
peratures from  o  to  30  Fah.  The  ammonia  condensing  coils 
are  in  some  cases  immersed  in  water,  which  is  renewed  in  order 
to  maintain  the  temperature  as  low  as  convenient,  while  in  otlier 
cases  the  condensation  is  brought  about  by  allowing  a  spray  of 
water  to  fall  over  them  from  top  to  bottom. 

Except  for  details  of  the  apparatus  employed,  the  principles 
outlined  above,  as  well  as  the  leading  features  of  the  equipment, 
•are  the  same  for  a  variety  of  substances  which  may  be  used  as 
refrigerating  agents. 

Thus,  sulphur  dioxide,  carbon  dioxide,  sulphuric  ether,  me- 
thylic  ether  and  still  more  recently  liquid  air  may  be  and  have 
been  used  in  the  general  manner  above  described. 

Sec.  89.   PRINCIPAL  FEATURES  OF  AMMONIA 
REFRIGERATING  APPARATUS. 

In  Fig.  298  is  shown  diagramatically  the  arrangement  of  ap- 
paratus in  the  De  La  Vergne  system  of  ammonia  refrigeration. 
In  all  such  systems  involving  the  compression  of  a  gas  it  is  most 
important  that  the  compressed  gas  be  as  completely  discharged 
as  possible  at  Hie  end  of  the  stroke,  else  it  will  re-expand  on  the 
return  stroke,  thus  preventing  the  inflow  of  a  full  charge  of  fresh 
gas  and  thus  reducing  the  effective  capacity  of  the  machine.  In 
the  system  illustrated  in  these  figures  this  is  accomplished  by  in- 
jecting into  the  compressor  at  each  stroke  a  certain  quantity  of 
oil  which  fills  all  clearances  and  thus  insures  the  delivery  of  prac- 
tically the  entire  charge  of  gas.  This  oil  likewise  acts  to  lubri- 


550  PRACTICAL  MARINE  ENGINEERING. 

cate  the  moving  parts  and  to  seal  the  stuffing-box,  piston  and 
valves,  and  thus  to  prevent  leakage,.  It  also  acts  to  some  extent 
to  absorb  the  heat  resulting  from  compression,  thus  to  reduce 
the  expenditure  of  work  required.  In  Fig.  299  is  shown  the 
double  acting  compression  cylinder  used  in  this  system.  The 
two  passages  marked  "Suction"  and  "Discharge,"  respectively, 
connect  the  compressor  with  the  pipe  system. 

On  the  up  stroke  gas  flows  through  the  lower  suction  valve 
into  the  space  behind  the  moving  piston,  while  the  gas  above  the 
piston,  after  being  compressed  to  the  condenser  pressure,  is  dis- 
charged through  the  upper  valves  (in  the  loose  head)  into  the 
discharge  passage. 

On  the  down  stroke  gas  flows  into  the  cylinder  through  the 


AMMONIABCONDENSER 


Fig.  298.    Diagram  Showing  Arrangement  of  Ammonia  Refrigerating  Machinery. 

upper  suction  valve,  and  the  gas  below  the  piston  is  compressed 
and  passes  through  the  lower  discharge  valves  into  the  discharge 
passage.  The  piston  in  its  downward  course  closes  successively 
the  openings  of  these  two  discharge  valves.  When  the  lower  is 
closed,  however,  the  upper  one  communicates  with  the  chamber 
in  the  piston,  and  the  gas  and  oil  still  remaining  below  the  piston 
are  discharged  through  its  valves  into  the  chanfber  and  out  by 
the  upper  discharge  valve. 

The  oil  is  injected  directly  into  the  compressor  after  the 
compression  of  the  full  cylinder  of  gas  has  commenced,  and  thus 
does  not  reduce  the  capacity  of  the  machine. 

The  compressed  gas  and  oil  thus  delivered  from  the  com- 
pressor cylinder  pass  on  to  the  oil  cooler.  The  cooled  oil  drops 


REFRIGERATION. 


55i 


into  the  bottom  of  the  tank,  while  the  gas  continues  into  the  con- 
denser, where  it  is  liquified  and  collected  in  a  second  tank.  Two 
forms  of  condenser  may  be  employed.  In  one  form  the  con- 
densing coils  are  immersed  in  a  tank  of  cold  water,  which,  by 
suitable  pumping  arrangements,  is  continuously  withdrawn  and 
renewed  in  order  to  maintain  as  low  a  temperature  as  convenient. 
In  the  other  form  of  condenser  water  is  sprayed  over  the  coils, 
falling  from  top  to  bottom,  while  the  gas  enters  preferably  at  the 


Marine '£ngintcrin0 

Fig.  299.    Ammonia  Compressor  Cylinder.       Fig.  300.    Ammonia  Compressor  Cylinder. 

bottom  and  passes  upward  in  a  direction  opposite  to  that  of  the 
water.  The  latter  type  of  condenser  is  the  more  efficient  of  the 
two  for  the  same  amount  of  water,  while  it  has  the  further  ad- 
vantage that  ammonia  leaks  are  readily  detected  by  the  odor, 
while  with  the  submerged  condenser  the  escaping  gas  is  ab- 
sorbed by  the  water,  and  its  escape  is  not  so  readily  noted. 

From  the  collecting  tank  the  liquid  ammonia  passes  through 


552  PRACTICAL  MARINE  ENGINEERING. 

the  expansion  cock  into  the  expansion  coils.  The  latter  may  be 
located  directly  within  the  space  to  be  refrigerated,  or  they  may 
be  surrounded  by  a  brine,  which  in  turn  is  pumped  through  the  re- 
frigerating coils  proper.  The  former  method  is  the  more  efficient 
inasmuch  as  a  loss  always  attends  a  multiplication  of  such  pro- 
cesses. The  chief  objection  to  this  method  lies  in  the  somewhat 
greater  liability  of  ammonia  leaks  and  the  resulting  presence  of 
ammonia  in  places  where  it  may  be  objectionable.  The  expan- 
sion cock  must  be  capable  of  nice  adjustment  in  order  to  make 
possible  the  proper  control  of  the  flow  of  liquid  ammonia  into  the 
coils.  In  the  system  here  shown  this  is  accomplished  by  making 
the  orifice  on  the  delivery  side  of  the  cock  m  the  shape  of  a  very 
narrow  wedge,  the  point  of  which  is  the  first  to  open.  Move- 
ment  is  then  imparted  to  the  plug  by  a  worm  and  wheel,  thus  in- 
suring adjustment  of  the  most  delicate  character. 

The  point  of  chief  importance  in  connection  with  the  expan- 
sion coils,  and,  in  fact,  in  connection  with  the  entire  piping  sys- 
tem, is  that  of  the  joints.  Screwed  connections  are  far  more  lia- 
ble to  leak  under  ammonia  than  under  steam,  and  the  utmost 
care  is  needed  in  regard  to  this  feature.  For  the  best  results 
special  joints  are  required.  In  a  representative  joint  of  this  char- 
acter the  thread  into  which  the  pipe  screws  does  not  reach  en- 
tirely to  the  outside  of  the  fitting,  but  instead  a  smooth  annular 
space  is  provided  around  the  pipe  beyond  the  termination  of  the 
thread.  This  recess  is  filled  with  solder,  the  pipe  and  fitting  be- 
ing well  tinned,  and  thus  a  screwed  and  soldered  joint  is  made 
which  is  found  tight  against  ammonia  under  all  pressures  em- 
ployed. 

The  cooling  efficiency  of  the  refrigerating  coils  is  also  much 
increased  by  clamping  to  the  pipes  thin  disks  of  cast  iron.  These 
disks  are  made  in  halves,  and  are  placed  at  intervals  of  6  to  10 
inches  on  the  pipes.  They  effect  an  increase  in  the  surface  in 
contact  with  the  air,  and  thus  an  increase  in  the  heat,  which  can 
be  withdrawn  from  the  air  and  conducted  to  the  cooling  sub- 
stance within  the  pipe. 

In  the  Eclipse  system  of  refrigerating  machinery  the  same 
general  principles  are  involved,  but  with  some  differences  in  the 
apparatus  employed.  The  compressor,  as  shown  in  Fig.  300,  is 
single  acting,  the  gas  being  compressed  on  the  upper  side  of  the 
piston  only.  No  oil  is  used  to  fill  the  clearance  spaces,  and  the 
clearance  is  reduced  to  a  negligible  quantity  by  working  the 


REFRJGERA  TION.  553 

piston  almost  metal  and  metal  against  the  head.  This  is  made 
practicable  by  making  the  pump  head  movable  so  that  it  may  op- 
erate as  a  large  valve  the  full  size  of  the  bore  of  the  cylinder,  and 
through  the  seat  of  which,  if  need  be,  the  piston  might  pass 
without  injury.  Under  normal  conditions  this  entire  head  does 
not  work  as  a  valve,  the  discharge  being  through  a  small  steel 
valve  in  the  center  of  the  head,  as  shown  in  the  figure.  The  com- 
pressor cylinder  is  surrounded  with  the  water  jacket,  which  ab- 
sorbs a  part  of  the  heat  generated  by  the  compression  of  the  gas. 
For  controling  the  expansion  in  this  system  a  special  form  of 
valve  is  used  which  provides  for  close  adjustment  of  the  opening 
and  is  fitted  with  an  index  and  pointer  so  that  the  amount  of 
opening  may  be  ascertained  and  such  adjustments  made  as  have 
been  by  trial  found  to  best  suit  each  case. 

Sec.  90.    REFRIGERATION  BY  THE  EXPANSION 
OF  A  COMPRESSED  GAS. 

We  will  next  examine  the  principles  involved  in  the  use  of 
air  as  a  refrigerating  agent  through  compression,  cooling  and 
expansion. 

If  compressed  air  is  allowed  to  expand  against  a  resistance, 
thus  doing  work,  while  at  the  same  time  no  heat  is  allowed  to 
enter,  the  air  will  lose  a  part  of  its  heat,  the  equivalent  in  amount 
of  the  work  done.  That  is,  the  work  is  done  at  the  expense  of  the 
heat  in  the  air,  which  gives  it  up  as  called  for  and  becomes  cor- 
respondingly cooled  in  consequence.  Thus,  for  example,  if  air  at 
100  pounds  absolute  pressure  and  at  a  temperature  of  70  degrees 
were  allowed  to  expand  to  15  pounds  pressure,  and  no  heat  be 
permitted  to  enter,  the  temperature  would  become  reduced  by 
about  220  degrees,  or  to  about  150  degrees  below  zero. 

Actually  the  absorption  of  some  heat  could  not  be  avoided, 
and  hence  the  actual  temperature  reached  would  be  higher  than 
thus  indicated.  The  equipment  for  utilizing  these  properties  of 
air  is  substantially  as  follows  : 

(i)  A  cylinder  in  which  air  is  drawn  from  the  atmosphere  or 
from  the  refrigerating  coils  and  compressed.  The  air  thus  be- 
comes heated  and  its  temperature  is  raised.  It  is  therefore  sent 
next  to  (2),  a  cooling  coil  working  after  the  manner  of  a  surface 
condenser  for  steam,  or  for  ammonia  vapor,  as  above  described. 
The  difference  here  is,  however,  that  no  effort  is  made  to  con- 
dense the  air,  but  simply  to  cool  it  down  to  somewhere  about  at- 


554  PRACTICAL  MARINE  ENGINEERING. 

mospheric  temperature.  The  air  is  next  sent  to  (3),  a  cylinder  in 
which  the  air  expands  and  does  work  and  becomes  thereby 
cooled.  From  this  cylinder  the  cooled  air  on  the  return  stroke  is 
forced  out  through  the  refrigerating  coils,  and  thus  the  cooling 
action  is  brought  about.  The  compression  and  expansion  cylin- 
ders are  connected  to  the  same  crank  shaft  in  such  manner  that 
the  work  done  by  the  expanding  air  will  aid  in  effecting  the  com- 
pression of  the  incoming  fresh  charge.  The  difference  in  the 
work  of  compression  and  that  furnished  by  expansion  plus  the 
friction  of  the  machine  must  be  made  up  by  the  motor  operating 
the  machine. 

Sec.  91.    PRINCIPAL  FEATURES  OP  COMPRESSED 
AIR  REFRIGERATING  APPARATUS. 

We  will  now  briefly  describe  the  leading  features  of  the 
Allen  dense-air  refrigerating  machine  as  illustrating  this  type  of 
apparatus. 

Experiment  has  shown  the  advantage  of  using  relatively 
high  pressures  throughout  the  apparatus.  The  air  in  the  refriger- 
ating coils  is  therefore  kept  at  about  60  Ibs.  gauge  pressure. 

From  these  coils  the  compressor  cylinder  draws  its  air, 
which  is  then  compressed  to  200  Ibs.  or  over,  and  this,  after  cool- 
ing, is  again  expanded  back  to  60  Ibs.  and  sent  to  the  coils  again, 
so  rhat  the  same  air  is  used  over  and  over.  To  make  up  for  leak- 
age a  small  air  compressor  is  added,  capable  of  delivering  air  at 
the  lower  pressure  into  the  inflow  pipe  leading  to  the  main  com- 
pressor. Again  the  cold  air  on  its  way  back  from  the  coils  at 
a  temperature  usually  below  freezing  is  used  in  a  special  cooler 
to  further  cool  the  compressed  air  at  high  pressure  before  it  is 
sent  to  the  expansion  cylinder. 

Referring  to  Fig.  301,  the  following  are  features  of  the  cyl- 
inder with  their  uses : 

(A)  the  steam  cylinder  which  furnishes  the  power  required. 

(B)  The    air    compressor    cylinder.      This    is    usually    sur- 
rounded by  a  water  jacket  to  assist  in  cooling  the  air  as  it  is 
compressed. 

(C)  The  cooling  coil  surrounded  by  water.     Through  this 
the  air  passes  and  thus  becomes  cooled  nearly  to  the  tempera- 
ture of  the  external  air. 

(D)  The  return  air  cooler  for  still  further  cooling  the  com- 
pressed air  by  allowing  it  to  give  a  part  of  its  heat  to  the  air  re- 


REFRIGERATION. 


555 


turning  from  the  refrigerating  coils  to  the  compressor  inflow,  as 
noted  above. 

(E)  The  expansion  cylinder.    The  cooled  air  is  admitted  to 
about  one-third  stroke  and  is  then  cut  off.    The  charge  is  thus 
expanded  to  about  three  times  its  original  volume,  and  is  thus 
brought  to  about  the  same  pressure  as  it  had  when  entering  the 
compressor  cylinder,  but  at  a  much  lower  temperature.     The 
air  is  then  discharged  through  a  pipe  which  leads  it  to  the  re- 
frigerating coils  or  to  the  point  where  its  capacity  for  absorbing 
heat  is  to  be  utilized. 

(F)  A  trap  through  which  the  air  passes  after  leaving  the 


Fig.  301.    Diagram  Showing  Arrangement  of  Compressed  Air  Refrigerating  Machinery. 

expansion  cylinder  and  in  which  are  gathered  the  lubricating 
oil  carried  by  the  air  from  the  compressor  cylinder  as  well  as  the 
frost  which  results  from  the  freezing  of  the  moisture  in  the  air. 
This  leaves  the  air  pure  and  dry  and  in  the  best  possible  condi- 
tion for  carrying  out  the  refrigeration  in  the  coils  beyond. 

(G)  A  pump  for  supplying  water  for  the  water  jacket 
around  the  compressor  cylinder,  for  the  bath  around  the  cooling 
coils  (C),  and  for  the  trap  (I). 

(H)  A  small  air  compressor  for  supplying  the  loss  due  to 
leakage. 

(I)  A  trap  for  taking  the  moisture  from  this  supplementary 
air  supply  so  as  to  have  it  enter  the  machine  as  dry  as  possible. 


556  PRACTICAL  MARINE  ENGINEERING. 

Sec.  92.    OPERATION    AND   CARE  OF  REFRIGERATING 

MACHINERY. 

Before  starting  refrigerating  machinery,  whether  newly  in- 
stalled or  after  any  considerable  period  of  disuse,  all  piping  and 
joints  should  be  tested  for  leaks.  This  may  be  done,  no  matter 
what  the  system  be,  using  the  compression  pump  to  compress 
air  into  the  piping  up  to  whatever  pressure  may  be  considered 
suitable.  The  seriousness  of  the  leakage  may  then  be  estimated 
by  the  rapidity  with  which  the  pressure  is  lost  after  allowing 
the  pump  to  stop.  The  larger  leaks  may  be  determined  by  the 
noise  made  by  the  escaping  air.  For  the  smaller  ones  the  joints 
are  sometimes  covered  with  soap-suds  so  that  the  escaping  air 
may  show  itself  by  blowing  a  cluster  of  bubbles.  After  the 
points  which  may  show  leaks  have  received  proper  attention,  the 
system  should,  for  a  considerable  time,  hold  the  pressure  without 
sensible  loss.  In  this  connection,  however,  it  must  be  remem- 
bered that  the  air  as  it  leaves  the  compressor  will  be  heated  by 
the  work  of  compression,  and  as  it  loses  this  excess  heat  in  the 
coils  there  will  tfe  a  corresponding  loss  cf  pressure.  After 
equality  of  temperature  with  the  outside  air  has  been  reached, 
however,  the  further  loss  of  pressure  should  not  be  appreciable. 
With  an  air  refrigerating  plant  the  presence  of  leaks  is  of  course 
of  less  importance  than  with  ammonia.  In  the  former  a  leak 
may  result  in  a  slight  decrease  in  the  capacity  of  the  machine, 
while  in  the  latter  the  capacity  of  the  machine  is  not  only  af- 
fected, but  ammonia  will  be  lost  as  well.  With  the  air  machine 
no  further  preliminaries  are  needed  beyond  the  examination 
necessary  to  insure  the  proper  mechanical  condition  of  the 
compressor  "and  steam  cylinders.  With  the  ammonia  machine, 
however,  it  is  necessary  next  to  exhaust  the  air  from  the  entire 
system  by  working  the  pumps  and  discharging  through  valves 
provided  for  this  purpose.  When  the  gauges  show  the  highest 
vacuum  which  can  be  maintained,  the  valves  are  closed  and  the 
system  is  ready  for  charging. 

The  ammonia  is  usually  provided  in  steel  flasks  containing 
a  known  weight  of  the  liquid.  To  introduce  the  charge  the  flask 
is  connected  to  the  charging  valve  according  to  the  directions 
which  usually  accompany  them.  In  the  meantime  the  machine 
is  run  at  slow  speed  with  the  suction  and  discharge  valves  open 
and  the  condenser  ready  for  operation.  The  expansion  valve  is 
then  closed  and  the  valve  of  the  flask  opened,  thus  allowing  the 


REPRIGERA  TION.  557 

ammonia  to  be  exhausted  into  the  system.  In  this  manner  one 
flask  after  another  is  exhausted  into  the  system  until  the  liquid 
shows  to  a  suitable  height  in  the  glass  gauge  of  the  receiver. 
The  charging  valve  is  then  closed  and  the  expansion  valve 
opened  and  regulated  until  with  the  machine  running  at  a  nor- 
mal speed  the  pressure  gauges  steady  down  to  the  pressures 
usually  maintained,  as  mentioned  in  Sec.  88,  and  a  frosting  of 
all  parts  of  the  expansion  coils  in  contact  with  the  air  shows 
that  the  refrigerating  action  is  in  vigorous  operation.  The 
weight  of  ammonia  in  the  flask  being  known,  its  complete  dis- 
charge may  be  determined  by  weighing  before  and  after  con- 
nection with  the  machine. 

For  the  routine  care  of  refrigerating  machinery  the  same 
principles  apply  as  for  steam  engines  and  pumping  machinery  in 
general,  and  they  need  not  be  here  repeated  in  detail.  A  few 
special  points  may,  however,  be  mentioned. 

In  ammonia  machinery,  through  leaky  stuffing-boxes  and 
in  other  ways,  air  may  occasionaly  find  its  way  into  the  system. 
Its  presence  will  decrease  the  efficiency  of  the  machine,  and  it 
must  therefore  be  removed  as  soon  as  possible.  The  most  no- 
ticeable symptoms  of  such  trouble  will  probably  be  a  rise  in  the* 
condenser  pressure.  Purging  valves  are  usually  fitted  on  the 
condenser  or  elsewhere  through  which  such  air  may  be  drawn 
off.  To  this  end  it  is  desirable  to  stop  the  machine  for  a  time  to 
allow  the  air  to  collect.  It  may  be  then  drawn  off  through  a 
rubber  hose  or  other  suitable  means  and  discharged  under 
water.  The  rise  of  bubbles  will  show  that  air  is  escaping,  while 
on  the  other  hand  the  presence  of  crackling  or  snapping  sounds 
will  indicate  that  the  air  is  all  exhausted  and  that  ammonia  is 
escaping  and  being  absorbed  by  the  water. 

Reference  has  been  made  to  the  importance  of  joints  and 
piping.  This  part  of  the  system  must  receive  especial  care  both 
in  the  original  installation  and  in  the  routine  attention.  For 
ammonia  in  particular,  as  already  noted,  special  joints  are 
usually  required,  and  both  ammonia  and  air  will  find  smaller 
leaks  than  steam.  It  must  also  be  remembered  that  the  chemi- 
cal action  between  ammonia  and  copper  renders  impossible  the 
use  of  copper,  brass  or  bronze  through  all  parts  of  the  installa- 
tion with  which  the  ammonia  may  come  in  contact. 

With  compressed  air  refrigerating  machinery  it  sometimes 
happens  that  the  ports  or  passages  through  which  the  air  first 


558  PRACTICAL  MARINE  ENGINEERING. 

passes  in  its  expansion  become  clogged  with  a  deposit  of  snow 
or  ice,  due  to  the  freezing  out  of  the  moisture  contained  in  the 
air.  In  the  Allen  dense-air  machinery,  where  the  same  air  is  used 
over  and  over  again,  additional  moisture  can  only  come  from  the 
small  make  up  air  supply,  and  most  of  this  is  removed  by  the 
trap  provided  for  this  purpose.  In  operation  this  trap  should  be 
watched  in  order  to  make  sure  that  its  action  is  efficient  and 
that  there  is  no  danger  of  the  passage  of  water  over  into  the  ex- 
pansion system.  In  routine  operation  it  is  usually  desirable  to 
clean  the  machine  by  heating  it  up  and  blowing  out  all  the  oil 
and  ice  deposits.  To  this  end  the  valves  in  the  main  pipes  lead- 
ing the  air  to  and  from  the  coils  are  closed,  thus  shutting  off  the 
machine  from  the  remainder  of  the  system.  A  by-pass  is  then 
opened,  connecting  the  main  expansion  pipe  beyond  the  oil  and 
snow  trap  with  the  main  return  from  the  coils.  Connections 
are  then  opened  in  the  so-called  hot  air  pipe  leading  from  the 
compressor  cylinder  to  the  expander  cylinder,  and  the  expander 
inlet  valve  Is  partly  closed.  Live  steam  is  then  let  slowly  into 
the  jacket  of  the  oil  trap  in  order  to  thaw  out  all  ice  and  hard- 
ened oil,  and  the  machine  is  run  moderately  for  a  time,  during 
which  the  blow  off  valves  of  the  trap  and  expander  cylinder  are 
frequently  opened  until  everything  appears  clean.  Then  the 
machine  is  readjusted  to  its  normal  condition  and  run  as  before. 
If  it  should  be  suspected  that  any  considerable  quantity  of 
oil  and  water  have  gotten  into  the  pipe  system  and  are  clog- 
ging the  surfaces,  the  pipes  may  be  cleaned  by  running  hot  air 
through  them  and  drawing  off  the  oil  and  water  at  the  bottom 
of  the  manifolds  of  the  refrigerating  coils. 


ELECTRICITY  ON  SHIPBOARD.  559 


CHAPTER  XII. 
ELECTRICITY  ON  SHIPBOARD. 

Sec.  93.  INTRODUCTORY. 

In  the  present  chapter  we  shall  discuss  briefly  and  from  the 
practical  standpoint  the  application  of  electricity  on  board  ship 
for  lighting,  and  as  a  source  of  auxiliary  power.  The  limitations 
of  space  prevent,  of  course,  the  development  of  the  subject  in 
detail,  and  we  shall  therefore  give  by  way  of  introduction  a  few 


/         /  V  \ 

t    ,' 
/ 


t 


Fig.  302.      Simple  Bar  Magnet,  Showing  Lines  of  Force. 

statements  and  definitions  which  must  be  taken  for  granted  by 
those  not  already  familiar  with  the  elements  of  electrical  theory. 

(i)'We  first  suppose  that  the  reader  is  familiar  with  a  com- 
mon magnet  and  its  more  well-known  properties. 

(2)  The  name  magnetic  field  is  applied  to  the  space  around 

a  magnet  and  through  which  the  magnetic  forces  act.    Let  PQ, 

Fig.  302,  be  a  magnet,  with  one  pole  at  E  and  one  at  A,  and  sup- 


560 


PRACTICAL  MARINE  ENGINEERING. 


pose  the  latter  to  correspond  to  the  north  end  of  a  compass 
needle. 

It  must  be  understood  that  the  magnetic  forces  act  really  in 
closed  paths,  as  indicated  by  the  dotted  lines  in  the  figure.  That 
is,  if  we  should  map  out  the  direction  in  which  the  north  end  of 
a  long,  thin  magnet  would  be  urged,  beginning  with  A,  we  should 
trace  out  a  path  ABCDE.  That  is,  a!  north  magnet  pole,  if  free 
to  move  by  itself,  would  tend  to  move  along  the  path  from  A 
around  to  E,  in  the  direction  of  the  arrow,  and  would  so  move 
unless  prevented  by  some  external  force.  Hence  the  magnetic 
force  acts  all  along  this  line  from  one  end  to  the  other,  thus  mark- 
ing out  what  is  called  a  line  of  force.  Now,  to  complete  the  cir- 
cuit it  is  considered  that  the  same  force  acts  on  through  from  E 


Marine  Engineering 


Fig.  303.     Horseshoe  or  Bent  Magnet,  Showing  Lines  of  Force. 

to  A  inside  the  iron  or  steel,  although  we  are  not  able  to  measure 
the  actual  force  there  in  the  ordinary  way.  The  entire  space 
around  and  within  a  magnet  is  thus  occupied  with  these  lines  of 
force,  and  in  its  widest  sense  therefore  the  magnetic  field,  or  field 
of  force  of  a  magnet,  would  include  all  space.  As  we  move  away 
from  the  immediate  vicinity  of  the  poles,  however,  the  force  be- 
comes weaker  and  weaker,  and  finally  at  no  great  distance  be- 
comes very  small.  Practically, then,  the  field  of  force  includes  only 
that  part  of  space  within  which  the  magnetic  forces  are  measur- 
ably large  in  amount.  By  changing  the  form  of  the  magnet,  as 
in  Fig.  303,  the  sensible  part  of  the  field  becomes  limited  to  the 
space  between  the  two  poles,  as  shown  by  the  dotted  lines,  and  it 
also  becomes  quite  uniform  in  strength. 


ELECTRICITY  ON  SHIPBOARD.  561 

(3)  All  the  phenomena  connected  with  what  we  call  electric 
currents  in  wires  or  other  conductors  take  place  as  though  a  cur. 
rent  of  something  was  flowing  around  the  closed  circuit.    Scien- 
tists do  not  assume  that  there  is  in  reality  anything  actually  flow- 
ing within  the  wire.    In  fact,  the  nature  of  electricity  and  of  the 
electric  current  are  not  satisfactorily  known,  and  so  in  the  ab- 
sence of  more  definite  information  we  speak  of  the  electric  current 
simply  as  an  aid  in  the  discussion. 

(4)  The  fundamental  principle  which  seems  to  connect  mag- 
netism with  electric  currents  is  found  in  the  following  fact : 

A  wire  or  conductor  in  which  an  electric  current  is  flowing 
is  surrounded  by  a  field  of  magnetic  force,  as  shown  in  Fig.  304. 
If  the  current  is  flowing  away  from  the  observer,  or  along  the 
direction  in  which  he  looks,  then  the  direction  of  the  force  is  such 
that  a  free  north  magnetic  pole  would  tend  to  go  round  and  round 
the  wire  in  circular  paths  in  the  direction  shown  by  the  dotted 
lines. 


..>-._\Vv-//7 

C^S 

.Marine  Engineering 

Fig.  304.      Lines  of  Force  About  a  Wire  Carrying  an  Electric  Current. 

\ 

(5)  If  we  bend  the  wire  in  wrhich  the  current  is  flowing  into 
the  form  of  a  circle,  as  in  Fig.  305,  then  these  separate  effects 
combine  and  we  have  a  field  of  force  just  the  same  as  though  the 
wire  circuit  were  a  very  short,  flat  magnet,  the  two  poles  being 
very  close  together.  If  we  have  many  turns  of  wire  on  a  spool 
then  all  these  effects  are  added,  and  we  have  a  magnetic  field  of 
still  greater  force  and  distributed  almost  exactly  as  though  the 
core  of  the  spool  were  a  bar  magnet.  If,  in  fact,  we  put  in  a  piece 
of  soft  iron  for  the  core  of  the  spool,  then  we  shall  find  that  the 
iron  itself  becomes  magnetised,  and  adds  its  force  to  that  of  the 
current,  thus  producing  a  still  stronger  field  of  force.  A  rather 
more  exact  way  of  stating  this  is  to  say  that  the  current  which 
flows  tends  to  produce  a  magnetic  field,  but  that  there  is  a  certain 
resistance  to  the  setting  up  of  this  force,  and  that  this  resistance 
depends  on  the  substance  through  which  it  is  to  be  set  up.  If 
there  is  no  metal  core,  then  the  magnetic  force  must  pass  through 


562  PRACTICAL  MARINE  ENGINEERING. 

air  around  the  entire  circuit.  It  so  happens  that  the  resistance  to 
the  setting  up  of  magnetic  forces  is  very  much  less  in  iron  than  in 
air,  so  that  if  an  iron  core  is  put  in,  the  total  resistance  in  the  cir- 
cuit of  the  magnetic  forces  is  very  much  reduced,  and  the  same 
electric  current  can  then  set  up  a  much  stronger  field  than 
through  air  all  the  way. 

(6)  We  can  now  state  the  fundamental  principle  upon  which 
the  operation  of  the  electric  generator  depends. 

If  a  wire  is  so  moved  as  to  cut  across1  the  lines  of  magnetic 
force,  then  there  will  be  generated  a  force  tending  to  set  up  a 
current  of  electricity  in  the  wire.  This  is  known  as  the  electro- 
motive force,  and  is  usually  abbreviated  into  E.M.F.  If,  then, 
the  ends  of  the  wire  are  connected  so  as  to  form  a  closed  circuit, 


A 

Fig.  305.     Lines  of  Force  About  a  Coil  Carrying  an  Electric  Current. 

and  the  movement  is  such  that  the  amount  of  magnetic  force 
which  passes  through  the  circuit  of  the  wire  undergoes  a  change, 
either  increase  or  decrease,  then  a  current  of  electricity  will  be  set 
np  in  the  wire,  and  will  continue  as  long"  as  such  change  is  in 
progress.  Thus,  in  Fig.  306,  on  the  right,  if  the  loop  of  wire 
should  be  moved  from  a  strong  to  a  weak  field,  as  shown,  then 
the  amount  of  force  passing  through  the  circuit  would  decrease 
and  a  current  would  be  set  up,  as  shown,  and  lasting  as  long  as 
the  change  was  in  progress.  If,  further,  the  coil  should  move  on 
from  the  weak  to  a  strong  field,  there  being  no  change  in  the  di- 
rection of  the  lines  of  force,  then  a  current  would  be  developed 
in  the  opposite  direction  to  that  developed  by  the  movement 
from  strong  to  weak.  If,  however,  at  the  same  time  the  direction 


ELECTRICITY  ON  SHIPBOARD. 


563 


of  the  lines  of  force  should  change,  then  the  direction  of  the  cur- 
rent would  remain  unchanged,  as  shown  in  the  figure.  If  also,  as 
shown  on  the  left,  the  loop  were  to  be  turned  sideways,  so  that 
a  smaller  amount  of  force  could  pass  through,  then  also  a  current 
would  be  set  up  and  would  last  as  long  as  the  change  was  in 
progress. 

In  all  such  cases  the  direction  in  which  the  current  will  flow 
may  be  determined  by  the  following  rule :  If  we  look  at  the  loop 
along  the  lines  of  force  in  the  direction  in  which  a  free  north  mag- 
netic pole  would  tend  to  move,  and  the  change  in  the  amount  of 
force  passing  through  the  loop  is  a  decrease,  then  the  current  will 
flow  in  the  right-hand  direction,  or  with  the  hands  of  a  watch. 
If  the  change  of  force  is  an  increase,  the  current  will  of  course 
flow  in  the  opposite  direction. 

The  generation  of  electricity  in  all  forms  of  electric  gener- 


5^ 


777 


\ 


Fig.  3CKJ. 


Development  of  Electro-Motive  Force  by  Moving  a  Coil  of  Wire  in  a 
Magnetic  Field. 


ators,  and  its  use  in  all  forms  of  motors,  depends  fundamentally 
upon  the  few  principles  explained  above. 

Electro-Motive  Force.  —  The  force  in  answer  to  which  the  elec- 
tric current  is  set  up  and  maintained  is  known  as  the  electro-motive 
force.  Relative  to  the  electric  current  this  force  plays  a  part  quite 
similar  to  that  played  by  steam  pressure,  or  a  difference  of  steam 
pressures,  in  causing  a  flow  of  steam  from  one  place  to  another. 
In  fact,  the  term  electric  pressure,  or  difference  of  electric  pres- 
sures, is  now  quite  commonly  used  by  engineers  instead  of  elec- 
tro-motive force.  The  phrase  electro-motive  force  is  commonly 
abbreviated  to  E.M.F.  The  unit  of  E.M.F.  is  known  as  the  volt. 

Resistance.  —  The  electric  current,  in  flowing  around  the  cir- 
cuit, meets  with  a  certain  resistance,  and  it  is  in  fact  this  resist- 
ance which  the  E.M.F.  must  constantlv  overcome.  This  resist- 


564  PRACTICAL  MARINE  ENGINEERING. 

ance  to  the  flow  of  the  electric  current  may  be  likened  to  the 
resistance  of  a  pipe  to  the  flow  of  water  within  it. 

Electric  resistance  depends  on  the  material  of  the  circuit,  on 
its  length,  and  on  its  cross-sectional  area.  The  greater  the  length 
the  greater  the  resistance,  and  the  greater  the  cross-sectional  area 
the  less  the  resistance,  both  in  direct  proportion.  Substances 
are  usually  divided  into  conductors  and  non-conductors.  There 
is  no  substance  so  good  a  conductor,  however,  but  that  it  op- 
poses some  resistance  to  the  passage  of  a  current,  and  there  is 
no  non-conductor  so  perfect  that  it  will  not  allow  the  passage  of 
minute  currents,  especially  under  very  high  pressures. 

The  unit  of  resistance  is  called  the  Ohm,  and  is  defined  as  the 
resistance  which  is  opposed  to  the  passage  of  an  electric  current 
by  a  tube  of  pure  mercury  of  a  certain  size  and  length.*  The 
result,  then,  of  the  action  of  electro-motive-force  against  electric 
resistance  is  to  produce  an  electric  current,  and  the  unit  of  cur- 
rent thus  produced  is  called  the  Ampere.  This  is  defined  as  the 
current  which  will  be  produced  by  an  E.M.F.  of  one  Volt  acting 
through  a  resistance  of  one  Ohm.  It  signifies  a  certain  rate  of 
flow,  just  as  if  we  should  give  a  special  name  to  a  flow  of  say  20 
gallons  of  water  per  minute  through  a  pipe. 

Electric  Power  is  represented  by  the  product  of  E.M.F.  and 
rate  of  flow,  just  as  in  the  case  of  the  flow  of  water  in  a  pipe  it  is 
represented  by  the  product  of  the  pressure  per  square  foot  and 
the  rate  of  flow  expressed  in  cubic  feet. 

The  unit  of  electric  power  is  called  the  Watt,  and  is  the 
power  required  to  maintain  for  a  minute  a  flow  of  one  ampere 
under  a  pressure  of  one  volt.  Similarly  a  current  of  8  amperes 
under  a  pressure  of  50  volts  will  require  400  watts. 

To  connect  electric  with  mechanical  power  it  is  found  that  in 
round  numbers  746  watts  equals  one  horse  power.  This  must 
not  be  taken  to  mean  that  one  indicated  horse  power  in  a  steam 
engine  will  give  746  watts  in  a  generator.  There  are  losses  be- 
tween the  two  due  to  the  fact  that  the  electric  generator  cannot 
transform  all  the  mechanical  energy  it  receives  into  electric  en- 
ergy, and  thus  wastes  a  certain  amount,  which  appears  chiefly  as 
heat.  The  number  746  gives  the  ratio  which  would  exi^t  if  there 
were  no  losses  of  any  description  whatever. 


*  Cross  section  of  one  millimeter  square  or  about  1/25  inch,  and  length 
of  1063.  millimeters  or  about  42.  inches. 


ELECTRICITY  ON  SHIPBOARD.  565 

The  ordinary  commercial  unit  of  electric  power  is  the  kilo- 
watt, or  1,000  watts..  It  is  thus  equivalent  to  about  I  1-3  horse 
power  of  mechanical  work. 

Ohms  Law. — We  will  now  state  the  fundamental  law  which 
gives  the  relation  between  the  current,  the  E.M.F.  and  the  resist- 
ance. It  is  simply  that  the  current  in  amperes  equals  the  E.M.F 
in  volts  divided  by  the  resistance  in  Ohms,  or  in  symbols 

C  =  E  -f-  R  or  E  =  CR. 
Likewise,  if  we  denote  the  electric  power  by  P  we  have : 

P  =  CE  =  CR 

This  measures  the  power  which  is  required  to  maintain  the  cur- 
rent in  the  circuit.  If  no  other  effects  are  produced  it  is  wholly 
expended  in  heating  the  circuit,  and  the  heat  thus  developed  will 
be  measured  by  the  power  multiplied  by  the  time  or  in  symbols 

H=CRt. 

Now,  without  further  discussion  of  the  principles  of  electrical 
engineering,  we  will  proceed  to  a  brief  description  of  the  appar- 
atus more  commonly  met  with  on  shipboard. 

Sec.  94.    THE  DYNAMO. 

We  may  consider  the  dynamo  simply  as  an  apparatus  de- 
signed for  the  development  of  electric  current,  or  for  the  trans- 
formation of  mechanical  into  electrical  energy.  It  consists  essen- 
tially of  two  electro  magnets,  which  we  may  call  A  and  B.  A  is 
stationary,  and  between  its  poles  B  rotates,  carrying  its  coils  of 
wire  through  the  field  produced  by  A.  The  rotating  magnet  and 
its  coils  is  known  as  the  annaturc,  and  the  fixed  magnet  and 
coils  as  the  poles  and  field  coils.  In  Fig.  307  is  shown  one  of  the 
rotating  coils  A  of  the  armature,  while  its  successive  positions  are 
shown  by  i,  2,  3,  4.  The  field  of  force  due  to  the  field  coils  and 
poles  is  also  indicated  by  the  arrows.  In  accordance  with  the 
principles  above  stated  an  E.M.F.  is  thus  generated  in  the  arma- 
ture coils.  It  may  be  likewise  seen  that  the  E.M.F.  will  act  alter- 
nately in  opposite  directions  in  these  coils,  changing  as  their 
plane  is  about  midway  between  the  poles,  or  in  the  position  shown 
at  A.  All  these  elementary  forces  thus  generated  in  the  separate 
coils  of  an  actual  armature  are  gathered  together  and  produce  the 
full  pressure  at  the  terminals. 

Electric  generators  are  of  two  chief  varieties,  direct  and  alter- 
nating current.  In  the  latter  the  E.M.F.  generated  is  allowed  to 
produce  the  current  in  the  circuit  back  and  forth,  alternating  in 


566 


PRACTICAL  MARINE  ENGINEERING. 


direction  as  the  coils  pass  between  the  poles.  The  current  may 
thus  be  likened  to  a  series  of  surges  to  and  fro,  but  without  con- 
tinuous flow  in  either  direction.  In  the  former,  or  direct  current 
machine,  these  impulses  are  so  taken  up  by  the  commutator  that 
they  are  all  adjusted  or  turned  in  one  direction,  and  we  have, 
therefore,  a  continuous  flow  rather  than  a  series  of  surges  back 
and  forth. 

It  is  found  by  experience  that  either  form  may  be  used  for 
the  development  of  light  by  either  the  incandescent  or  arc  sys- 
tem, while  also  either,  by  the  use  of  appropriate  motors,  may  be 
used  for  the  development  of  mechanical  power. 


/ 

/ 

/ 

/ 

3 

v 

—  - 
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\ 

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\ 
V 

X 

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4 
Q 

~ 

0 

> 

o 

\ 

\ 

Mariiie  Engineering 

Fig.  307.      Action  of  Single  Coil  of  an  Electric  Generator. 

For  use  on  board  ship  the  direct  current  form  is  usually  em- 
ployed. A  discussion  of  the  relative  advantages  and  disadvant- 
ages of  the  two  forms  is  beyond  our  present  limits,  but  it  may  be 
said  in  a  word  that  for  lighting  the  limited  space  of  a  single  ship 
the  alternate  current  system  does  not  possess  the  advantages 
which  it  may  in  the  case  of  distribution  over  a  wider  area,  and  for 
the  operation  of  motors  its  use  would  entail  some  disadvantages 
and  complexity  from  which  the  direct  current  system  is  free. 

Restricting  our  attention  therefore  to  direct  current  machin- 
ery, the  simplest  is  found  in  the  so-called  series  dynamo.  In  this 


ELECTRICITY  ON  SHIPBOARD. 


567 


type  the  circuit  as  a  whole  leads  continuously  around  both  the 
armature  and  the  field  coils,  thence  into  the  external  circuit  at 
one  terminal,  and  around  back  to  the  machine  at  the  other  ter- 
minal. If  instead  of  this  arrangement  the  wires  are  lead  as  in 
Fig.  308,  the  current  leaving  the  armature  is  divided,  and  one 
part  flows  around  the  field  coils  while  the  other  goes  through  the 
external  circuit.  This  constitutes  the  so-called  shunt-wound  dy- 
namo. In  such  case  the  field  coils  consist  of  many  turns  of  fine 
wire,  while  in  a  series  machine  they  consist  of  a  few  turns  of 
larger  wire. 

A  combination  of  the  series  and  shunt-windings  constitutes 
the  so-called  compound  wound  machine.     For  the  purpose  of 


COMMUTATOR 


Marine  En<jince>-ing 

Fig.  308.      Shunt-Wound  Electric  Generator,  Outline  Diagram. 

delivering  a  constant  potential  or  electric  pressure  the  shunt- 
wound  machine  is  usually  employed,  and  it  is  this  type  which  is 
commonly  met  with  on  shipboard. 

We  will  now  pass  immediately  to  a  brief  description  of  a 
modern  electric  generator  applicable  to  marine  purposes. 

According  to  size  the  typical  marine  generator  is  made  with 
four  or  six  poles,  distributed  uniformly  around  the  circumference 
of  the  armature,  which  is  of  the  ring  type,  as  shown  in  Fig.  309. 
The  machine  is  shunt  wound  according  to  the  diagram  of  Fig. 
308.  The  commutator,  as  shown  in  Fig.  310,  consists  of  a  series  of 
bars  of  special  bronze  or  copper  formed  into  a  cylinder  or  drum, 


568 


PRACTICAL  MARINE  ENGINEERING. 


and  with  mica  or  other  insulating  material  between  them.  Each 
bar  of  the  commutator  is  joined  to  the  winding  on  the  armature, 
and  the  connections  are  such  that  the  E.M.F.  generated  in  the 


Fig.  309.      Ring  Armature. 


Marine  Enyineering 

Fig.  '310.      Commutator. 


entire  series  of  coils  is  so  directed  as  always  to  urge  the  current 
out  through  one  of  the  brushes  and  in  through  the  other.  The 
brushes  are  usually  in  the  form  of  a  block  of  carbon,  and  are 


ELECTRICITY  ON  SHIPBOARD. 


569 


carried  in  metal  holders,  as  shown  in  Fig.  311,  and  provided  with 
means  for  holding  them  by  adjustable  spring  pressure  up  to 
their  contact  with  the  commutator,  while  at  the  same  time  the 
frame  which  carries  them  may  be  rotated  as  a  whole  about  the 
axis  of  the  machine,  thus  bringing  them  to  bear  on  different  parts 
of  the  commutator  for  purposes  of  adjustment  with  varying  load. 
With  a  four-pole  machine  the  brushes  are  usually  placed  one 
nearly  on  top  and  one  at  about  right  angles.  This  makes  them 
more  accessible  than  if  placed  at  opposite  sides  of  the  commuta- 
tor, as  is  necessary  in  two-pole  machines. 


CLAMPING  SCREW 


BRUSH 

PRESSURE  SPRING 


\HARD  ROLLED 
COPPER  LEAVES 


ADJUSTING 
SCREW 


Fig.  311.      Brush  Holder. 

In  the  selection  of  such  a  generator  special  attention  should 
be  paid  to  points  of  mechanical  excellence,  especially  in  connec- 
tion with  the  bearings  and  balancing  of  the  armature,  the  con- 
struction of  the  brush  carriers,  the  binding  posts,  and  other  like 
points  entering  into  the  construction  of  the  generator  as  a  ma- 
chine. The  capacity  of  the  generator  should  be  such  that  it  will 
be  able  at  its  normal  rating  to  supply  the  expected  demand  foi 
light  and  power.  Generators  are  expected  to  be  able  to  stand 
a  certain  amount  of  over  load,  and  if  of  proper  design  and  in  a 


570  PRACTICAL  MARINE  ENGINEERING. 

\ 

cool  and  well  ventilated  -room  will  run  safely  at  far  above  their 
rated  power.  It  must  be  remembered,  however,  that  the  dynamo 
room  of  a  ship  is  rarely  cool  or  well  ventilated,  and  that  the  over- 
heating of  armature  and  field  coils  is  the  chief  limitation  on  the 
capacity  of  an  electric  generator.  Hence  in  the  unfavorable  situ- 
ation in  which  such  machines  are  usually  installed,  they  should 
not  be  expected  to  carry  any  considerable  over  load. 

The  typical  marine  generating  set  consists  of  a  generator 
as  above,  together  with  engine  set  on  one  base  and  coupled  direct 
together.  The  usual  number  of  revolutions  at  which  such  sets 
are  operated  ranges  from  perhaps  300  to  500,  according  to  size. 
The  engine  may  be  either  a  simple  or  compound,  or  even  a  triple- 
expansion,  though  the  latter  are  but  rarely  employed  in  marine 
practice.  In  the  design  and  construction  of  such  an  engine  the 
chief  points  to  be  held  in  view  are  solidity  and  strength,  espe- 
cially! in  the  running  parts,  but  without  undue  excess  of  weight, 
generous  bearing  surfaces  and  provision  for  continuous  and  sure 
supply  of  lubricant. 

With  such  small  high-speed  engines  the  presence  of  water 
in  the  cylinder  is  likely  to  produce  serious  damage,  and  especial 
care  should  be  taken  in  regard  to  the  relief  and  drainage  valves, 
both  hand  and  automatic  systems  being  preferably  fitted. 

The  governor  provided  with  such  engines  is  of  the  shaft  au- 
tomatic type,  and  should  control  the  revolutions  within  about  2 
per  cent,  for  change  from  full  load  to  no  load,  or  vice  versa. 

In  the  care  and  operation  of  such  engines  no  points  are  in- 
volved which  have  not  already  been  discussed  in  connection  with 
other  engines,  and  it  will  not  therefore  be  necessary  to  further 
consider  these  topics. 

MOTORS. 

Electric  motors  are  coming  into  use  on  shipboard  for  a 
variety  of  purposes  connected  with  the  application  of  auxiliary 
power,  but  chiefly  for  running  hoists  and  ventilating  fans.  It  will 
be  sufficient  for  our  present  purposes  to  note  that  a  motor  is  es- 
sentially the  same  as  a  generator,  and  only  differs  in  the  manner 
of  its  use.  With  the  latter  we  supply  mechanical  energy  and  with- 
draw electric  energy.  With  the  former  we  supply  electric  energy 
and  withdraw  mechanical  energy.  The  motor  contains  the  same 
parts  as  a  generator,  and  similarly  related,  and  differs  only  in 
being  thus  operated  in  the  inverse  manner  to  the  generator. 


ELECTRICITY  ON  SHIPBOARD.  571 

Sec.  95.   WIRING  AND  THE  DISTRIBUTION  OF  I/IGHT 
AND  POWER. 

The  conductors  used  for  the  distribution  of  electricity  may 
be  either  of  single  copper  wire,  varying  in  size  according  to  the 
current  to  be  carried,  or  of  several  small  wires  made  up  into  a 
cable  and  of  corresponding  capacity.  The  insulation  must  be  of 
extra  good  quality  in  order  to  stand  the  severe  conditions  to 
which  it  may  be  subjected  on  shipboard. 

The  materials  available  for  the  insulation  of  wire  are  rubber, 
either  gum  or  vulcanized,  gutta  percha,  and  various  special  com- 
pounds, together  with  braided  or  wrapped  coverings  of  cotton, 
linen  or  silk.  Gutta  percha  is  rarely  used  except  for  submarine 
cables  and  for  other  special  purposes.  It  must  be  understood 
that  none  of  these  substances  singly  and  no  combination  of  them 
is  a  perfect  non-conductor.  There  is  always  a  small  leakage 
through  the  insulation  and  air,  and  the  purpose  of  the  covering  is 
to  reduce  this  leakage  to  a  safely  negligible  amount.  For  marine 
work  it  is  especially  necessary  to  protect  the  insulation  against 
the  effects  of  dampness  and  corrosion,  as  under  these  influences 
deterioration  may  set  in,  causing  a  breaking  down  of  the  resist- 
ance to  the  passage  of  the  current  and  an  increase  in  the  leakage. 

The  usual  form  of  marine  lighting  wire  is  insulated  with  vul- 
canized rubber  or  other  special  compound,  covered  with  braided 
cotton,  the  whole  covered  with  a  coating  of  waterproof  and  pre- 
servative material.  For  switchboards  and  mountings  for  fixtures 
and  all  attachments,  slate,  marble  and  porcelain  are  used. 

The  conductors  are  run  either  in  iron  pipe  or  in  double 
wooden  mouldings.  The  former  or  the  conduit  system  is  to  be 
preferred,  as  the  conductors  are  thereby  given  the  protection  of 
the  iron  pipe.  The  conduit  system  is,  however,  much  more  ex- 
pensive than  the  moulding  system,  and  the  latter  is  therefore 
more  commonly  employed,  except  in  warship  work  and  where 
high  first  cost  is  not  an  objection. 

The  chief  point  in  either  system  is  to  give  to  the  wires  and  to 
the  various  junctions  and  connections  the  greatest  possible  pro- 
tection from  mechanical  injury  and  from  the  action  of  dampness 
and  water,  and  all  parts  of  the  distributing  system  exposed  to 
the  weather  or  to  the  sea  should  be  made  as  nearly  water-tight 
as  the  limitations  of  first  cost  will  permit. 

The  method  to  be  adopted  for  the  distribution  of  electricity 
depends  somewhat  on  the  purpose  for  which  it  is  to  be  used. 


572 


PRACTICAL  MARINE  ENGINEERING. 


The  most  common  use  on  board  ship  is  for  operating  incan- 
descent lamps,  where  as  nearly  as  may  be  the  same  pressure 
is  required  at  each  lamp.  For  this  purpose  the  so-called  dis- 
tribution in  parallel  is  required.  .  This  is  illustrated  by  the  dia- 
gram of  Fig.  312,  where  G  is  the  generator  and  //  the  lamps. 
It  is  seen  that  each  lamp  has  its  own  bridge  across  from  the  two 
mains  LL,  and  may  thus  be  turned  on  or  off  independent  of  the 
operation  of  the  others. 

In  the  early  days  of  electric  installations  on  shipboard  the 
iron  or  steel  hull  was  frequently  made  a  part  of  the  circuit,  or,  as 
it  was  sometimes  stated,  th^  return  was  made  through  the  hull. 
To  use  the  hull  in  this  way  it  was  simply  necessary  to  connect  one 


Marine  Enyinee.riny 

Fig.  312.      Distribution  in  Parallel. 


pole  of  the  generator  to  the  ship,  and  then  connect  one  lead  from 
each  lamp  to  the  hull  likewise. 

Great  difficulty,  however,  was  experienced  in  making  and 
keeping  good  contact  between  the  conductors  and  the  ship. 
Corrosion  was  especially  active  at  these  points,  and  they  were 
found  to  be  the  source  of  constant  trouble.  The  presence  of  stray 
current  returning  through  the  ship  was  also  believed  to  be  a 
factor  in  the  corrosion  and  deterioration  of  parts  of  the  ship's 
machinery. 

This  system  was  therefore  open  to  grave  objections,  and 
is  now  rarely  met  with.  The  modern  practice  is  to  employ  a  com- 
plete wire  conductor  for  the  external  circuit,  and  to  keep  the  cur- 
rent insulated  entirely  from  the  hull,  as  indicated  in  Fig.  312. 

Arc  lamps  are  very  commonly  operated  in  series,  as  shown 


ELECTRICITY  ON  SHIPBOARD.  573 

in  Fig.  313,  each  lamp  thus  receiving  the  same  current  which 
flows  around  the  entire  circuit.  On  board  ship  the  chief  or  only 
use  of  arc  lamps  is  for  the  searchlight,  and  the  number  there- 
fore will  usually  not  be  greater  than  one  or  two,  except  for 
warships,  where  a  larger  number  may  be  employed. 

We  may  also  need  current  supplied  at  various  special  points 
for  the  operation  of  motors  for  running  ventilators,  hoists,  etc. 

The  entire  distribution  may  therefore  comprise  various  cir- 
cuits according  to  the  use  to  be  made  of  the  current  and  the 
point  at  which  it  is  to  be  delivered.  It  is  furthermore  found 
desirable  to  split  up  the  incandescent  lighting  distribution  into 
a  series  of  circuits,  each  of  which  is  led  from  a  main  distributing 
point.  The  entire  distribution  will  thus  comprise  several  main 
circuits,  all  of  which,  however,  will  be  led  from  the  central  point. 

This  distribution  point  is  actually  furnished  by  the  sivitch- 


Fig.  313.      Distribution  in  Series. 

board,  a  slate  or  marble  slab,  on  which  are  mounted  the  various 
instruments,  switches,  circuit  breakers  and  connections  needful 
for  safely  carrying  out  the  distribution  in  the  various  ways  in 
which  it  may  be  required. 

We  will  now  refer  briefly  to  the  more  important  items  usu- 
ally grouped  on  the  switchboard : 

Switch  or  Cut  Out. — The  object  of  a  switch  or  cut  out  is  to 
break  the  circuit  and  thus  stop  the  flow  of  current.  With  a 
single  pole  switch  the  circuit  is  broken  at  one  point  only.  This 
is  the  usual  form  fitted  in  the  sockets  of  electric  lamps,  etc. 
With  a  double  pole  switch  the  circuit  is  broken  at  two  points. 
The  switches  mounted  on  the  switchboard  are  usually  of  this 
type,  and  are  to  be  preferred,  since  by  this  means  the  line  is 
entirely  cut  off  from  connection  with  the  generator. 


^74  PRACTICAL  MARINE  ENGINEERING. 

Fuses. — A  fuse  is  a  short  piece  of  fusible  alloy,  so  adapted 
to  the  proper  current  in  the  circuit  that  any  marked  increase  in 
•current  strength  will  cause  the  fuse  to  melt,  due  to  the  increase 
in  the  heating  effect.  The  result  of  this  will  be  a  break  in  the 
circuit  and  an  interruption  of  the  current. 

This  is  therefore  an  automatic  device  for  preventing  the  rise 
of  the  current  strength  beyond  a  certain  value.  In  the  same 
manner  as  with  switches,  we  may  have  single  pole  or  double 
pole  fuses.  The  latter  are  to  be  preferred,  as  they  give  a  double 
chance  of  breaking  the  circuit,  and  hence  a  greater  relative  mar- 
gin of  safety. 

Circuit  Breakers. — It  is  found  that  the  ordinary  fuse  does  not 
satisfactorily  provide  protection  against  momentary  variations  of 
current  strength  due  to  excessively  rapid  fluctuations  in  the  gen- 
erator or  in  the  outer  circuit.  To  prevent  possible  damage  from 
such  cause  a  magnetic  circuit  breaker  is  often  employed.  This 
consists  of  an  electro-magnet,  through  the  coil  of  which  the  main 
current  flows.  Any  sudden  increase  of  current  will  correspond- 
ingly increase  the  magnet  strength,  and  the  armature  is  so  ad- 
justed that  in  answer  to  this  excess  of  pull  it  will  move  toward 
the  magnet  poles,  thus  breaking  the  circuit  by  the  motion  pro- 
duced, and  interrupting  the  current  as  desired. 

Ammeter. — This  is  an  instrument  through  which  the  current 
is  passed  in  order  to  measure  or  indicate  its  strength.  The  in- 
dication is  shown  by  a  finger  moving  over  a  dial,  graduated 
usually  so  as  to  read  the  current  in  amperes.  The  Ammeter 
must  be  connected  in  series  with  the  machine  and  main  circuit. 

Volt  Meter. — This  is  an  instrument  which  measures  or  in- 
dicates the  E.M.F.  or  difference  of  electrical  pressure  between 
the  two  points  to  which  its  wires  are  attached.  It  serves  a  sim- 
ilar purpose  as  the  steam  gauge  for  the  boiler.  The  indication  is 
shown  by  a  finger  moving  over  a  dial  graduated  usually  so  as  to 
read  the  pressure  in  volts.  It  is  usually  connected  with  one  wire 
to  each  pole  of  the  generator  so  as  to  give  the  entire  pressure  in 
the  external  circuit. 

Rheostat. — This  is  simply  an  arrangement  for  varying  the 
total  resistance  of  the  external  circuit,  and  thus  of  varying  the 
pressure  available  for  that  part  beyond  the  instrument.  It  con- 
sists essentially  of  a  series  of  coils  of  wire,  more  or  less  of  which 
can  be  brought  in  and  made  a  part  of  the  circuit  by  moving  a 
handle  across  a  series  of  contact  points. 


ELECTRICITY  ON  SHIPBOARD.  575 

Rheostats  are  often  required  in  connection  with  the  use  of 
arc  lights,  or  with  the  governing  and  control  of  shunt-wound 
generators  and  motors. 

The  complete  installation  of  instruments,  switches,  connec- 
tions, etc.,  thus  brought  together  on  the  switchboard  has  as  its 
object  the  possibility  of  shifting  the  load  from  one  generator  to 
another,  of  connecting  the  various  circuits  singly  or  in  different 
combinations  with  any  one  or  any  combination  of  generators, 
and  at  the  same  time  providing  for  safety  and  for  the  proper 
measurement  of  the  pressure  and  current. 

Sec.  96.  I/AMPS. 

Electricity  is  used  on  shipboard  for  operating  incandescent 
or  glow  lamps  for  general  lighting,  for  operating  arc  lamps  for 
search-lights,  and  for  operating  motors. 

Incandescent  Lamps. — The  usual  style  of  incandescent  lamp 
consists  of  a  filament  of  carbon  in;  a  glass  bulb  exhausted  of  its 
air  and  sealed  air-tight.  The  carbon  filament  is  connected  to 
metal  terminals,  through  which  connection  with  the  external  cir- 
cuit is  made.  The  resistance  of  the  carbon  filament  is  very  high 
and  the  passage  of  the  current  gives  therefore  a  heating  effect, 
which  is  sufficient  to  raise  it  to  the  luminous  point.  If  the  air 
were  not  exhausted  from  the  bulb  the  carbon  would  be  imme- 
diately burned  up  or  converted  into  carbon  dioxide  by  union 
with  the  oxygen.  Since,  however,  the  oxygen  is  almost  entirely 
removed  such  combustion  is  limited  to  the  smallest  fraction  of 
the  filament  when  the  current  is  first  turned  on,  and  it  then  re- 
mains nearly  unchanged  for  a  period  of  time  ranging  from  600 
to  1,000  hours.  Gradually  the  filament  seems  to  disintegrate 
or  lose  its  strength,  and  finally  fails  by  snapping  in  two,  or  the 
bulb  becomes  blackened  by  a  deposit  of  carbon  on  its  inner  sur- 
face. The  usual  lamp  for  ship  fitting  is  one  of  16  candle  power, 
requiring  about  no  volts  pressure,  and  taking  about  y2  ampere 
of  current.  It  thus  follows  that  such  a  lamp  will  require  about 
55  watts  of  electrical  energy.  To  supply  this  will  require  the 
equivalent  of  not  far  from  75  at  the  steam  engine,  or  about  i-io 
H.P.  It  follows,  then,  that  we  may  expect  to  operate  roughly 
about  ten  such  lamps  per  I.  H.  P.  at  the  engine.  More  powerful 
lamps,  such  as  32  or  50  candle  power  will  require  more  current, 
and  hence  more  energy  and  more  horse  power  in  proportion. 

Arc  Lamps. — The  simplest  form  of  arc  lamp  is  shown  in 


576 


PRACTICAL  MARINE  ENGINEERING. 


Fig.  314.  It  consists  of  a  pair  of  carbon  rods,  separated  by  a 
slight  gap  as  indicated.  These  carbons  form  part  of  an  electric 
circuit,  which  is  completed  by  the  leads  to  the  generator,  as 
shown.  To  start  the  lamp  the  rods  must  be  brought  together, 
thus  completing  the  circuit  and  permitting  the  current  to  flow. 
The  instant  the  current  is  set  up,  however,  the  rods  are  separated 
a  slight  distance.  The  space  between  the  two  is  then  filled 
with  hot  air  and  carbon  dioxide,  and  across  this  the  current  is 
able  to  pass.  The  resistance  is  so  great,  however,  that  intense 
heat  is  developed,  and  this  brings  the  gases  and  the  particles  of 


N 


Marine  Engineering 

Fig.  314.      Arc  Lamp,  Simple  Form. 

carbon  which  are  torn  off  and  hurled  across  the  gap  all  to  a  state 
of  incandescence.  As  the  lamp  burns,  the  carbons  are  slowly 
consumed  and  the  gap  thus  widens.  There  is  always  some 
width  of  gap  for  which  the  lamp  operates  best,  and  a  constant 
adjustment  must  therefore  be  made.  It  is  found  further  that 
the  two  carbons  do  not  wear  equally  or  similarly. 

Referring  to  Fig.  314,  the  current  is  supposed  to  flow 
through  the  lamp  downward,  and  the  upper  or  positive  carbon 
will  then  wear  in  a  crater-like  form,  while  the  lower  or  negative 
carbon  will  take  a  more  rounded  or  pointed  form,  as  shown.  The 


ELECTRICITY  ON  SHIPBOARD.  577 

positive  end  will  also  wear  away  about  twice  as  fast  as  the  nega- 
tive end,  and  this  will  require  a  special  form  of  adjustment  in 
order  to  keep  the  gap  at  the  same  place  in  reference  to  a  lense  or 
mirror.  It  is  also  found  that  most  of  the  light  comes  from  the 
crater-like  cavity,  so  that  the  carbons  must  be  so  mounted  as  to 
allow  the  maximum  amount  of  light  to  escape  from  this  source. 

A  lamp  of  this  character,  mounted  and  provided  with  suit- 
able lenses  and  adjustments  for  controlling  the  carbons  and  for 
manipulating  and  turning  the  beam  of  light  in  any  direction  as 
desired,  constitutes  a  search-light,  as  installed  on  board  ship. 

We  shall  not  attempt  here  the  description  of  the  modes  of 
automatic  adjustment  for  the  carbons  or  of  the  optical  parts  of 
the  lamp,  as  the  present  purpose  is  to  give  only  a  general  idea 
of  the  engineering  side  of  the  problem. 

Such  lamps  require  a  pressure  of  from  50  to  60  volts  and  a 
current  of  from  50  to  150  amperes.  This  corresponds  to  from 
4  to  10  horse  power  at  the  lamp,  or  say  5  to  12  at  the  engine. 

Sec.     97.        OPERATION    AND     CARE     OF    EI/ECTRICAI, 

MACHINERY. 

[i]  Routine  Care. 

In  looking  over  a  generator  for  the  first  time  the  whole 
machine  should  be  carefully  examined,  both  as  to  its  electrical 
and  mechanical  features.  All  the  leads  of  the  wires  should  be 
followed  through  and  the  binding  posts  and  contacts  examined 
to  insure  that  they  are  in  proper  condition.  The  commutator 
and  brushes  should  be  carefully  looked  over  to  see  if  the  seg- 
ments of  the  former  are  in  good  condition,  and  if  the  surface  is 
smooth  and  free  from  scores  and  uneven  spots. 

Carbon  brushes  are  very  commonly  employed  in  modern 
marine  practice,  but  whatever  the  form  of  brush  the  fit  of  its 
end  on  the  commutator  should  be  noted,  and  if  necessary  it 
should  be  refitted  so  as  to  bed  suitably  on  the  surface.  The 
final  adjustment  of  the  brushes  cannot  be  made  until  the  ma- 
chine is  running,  but  the  adjusting  and  holding  devices  will  be 
carefully  examined  and  the  brushes  may  be  placed  in  approxi- 
mate adjustment,  according  to  judgment.  The  bearings  and 
journals  and  provision  for  oiling  should  then  be  examined,  and 
carefully  cleansed  if  the  condition  requires  it.  The  armature 
should  be  turned  by  hand  to  make  sure  that  there  is  the  neces- 


578  PRACTICAL  MARINE  ENGINEERING. 

sary  clearance  between  it  and  the  pole  pieces,  and  that  it  has  the 
proper  freedom  of  motion. 

These  various  points  having  been  attended  to  and  every- 
thing being  in  a  satisfactory  condition,  the  machine  may  be 
started.  A  shunt  machine  usually  excites  or  builds  up  best  when 
the  external  circuit  is  cut  out,  so  that  it  operates  simply  through 
its  own  armature  and  field  coil.    As  the  voltage  rises,  as  indi- 
cated on  the  voltmeter  or  pilot  lamp,  the  external  circuit  may 
be  switched  in  and  the  generator  will  then  settle  down  to  its 
work.     The  proper  lead  or  adjustment  of  the  brushes  is  the 
next  thing  to  be  attended  to.    This  must  be  ascertained  by  trial 
until  a  position  is  finally  found  where  the  sparking  is  reduced 
to  the  smallest  limits.    If  in  modern  machines  the  sparking  at 
the  brushes  is  in  any  degree  pronounced,  it  may  be  taken  as  a 
safe  indication   that  the   brush   adjustment   is   not   quite  as   it 
should  be.     The  exact  adjustment  will,  however,  vary  as  the 
load  changes,  and  hence  in  case  the  load  is  changing  rapidly 
there  will  be  more  sparking  than  with  a  steady  load. 

If  excessive  sparking  occurs  and  cannot  be  controlled  by 
the  brush  adjustment,  the  machine  should  be  shut  down  at  once, 
as  this  is  an  indication  that  it  is  out  of  electrical  balance,  and  to 
continue  running  it  would  mean  the  possibility  of  burning  out 
the  armature  or  seriously  injuring  the  commutator  and  brushes. 
In  some  cases  such  sparking  may  be  due  to  a  dirty  commu- 
tator, and  may  be  corrected  by  simply  cleaning  it.  The  pressure 
of  the  brushes  on  the  commutator  should  also  receive  attention, 
as  if  too  heavy  undue  wear  will  occur,  while  if  too  light  they  may 
jump  and  rur*  irregularly,  thus  causing  sparking. 

A  very  small  amount  of  lubricant  on  the  commutator  is 
usually  found  to  aid  in  smooth  running  and  in  saving  the  sur- 
face from  scoring.  In  amount  it  should  be  very  small,  a  drop  or 
two  of  hydrocarbon  oil  or  a  little  vaseline  or  a  rub  of  one  of  the 
standard  preparations  sold  for  the  purpose  is  sufficient. 

[2]  Faults. 

One  of  the  most  troublesome  features  connected  with  the 
operation  of  electric  machinery  is  the  possibility  of  the  occur- 
rence of  more  or  less  sudden  failure  at  some  point,  resulting  in 
the  sudden  extinction  of  a  certain  group  of  lights  or  the  stop- 
page of  a  motor,  or  even  the  interruption  of  the  entire  plant  in 
case  the  fault  lies  at  the  generator  itself. 


ELECTRICITY  ON  SHIPBOARD.  579 

In  all  such  cases  the  immediate  cause  of  the  trouble  is  the 
interruption  of  the  current,  either  in  whole  or  in  part.  This 
may  be  due  to  a  variety  of  causes,  as  follows :  (i)  The  resist- 
ance in  the  circuit  may  be  enormously  increased,  thus  cutting 
down  the  current  strength  proportionately.  (2)  The  current 
may  be  diverted  in  some  other  direction,  finding  an  easier  path, 
and  thus  avoiding  the  circuits  in  which  it  belongs.  (3)  The  gen- 
erator itself  may  fail  to  develop  the  necessary  E.M.F.,  and  hence 
while  the  circuits  may  be  in  perfect  condition  the  current  will  be 
weakened  in  corresponding  degree. 

The  increase  of  resistance  in  a  circuit  may  be  due  to  poor 
contact  at  binding  posts  or  junctions,  arising  from  improper 
mechanical  construction  or  fitting,  or  from  the  presence  of  oxide 
due  to  corrosion,  or  from  the  reduction  in  the  cross  section  of 
a  conductor  due  to  corrosion,  or  to  any  like  cause  which  de- 
creases the  cross  section  of  the  conductor  or  changes  its  electric 
conductivity.  In  case  the  conductor  is  broken  or  the  separation 
is  complete,  the  resistance  across  the  air  gap  becomes  prac- 
tically infinite,  and  the  current  is  completely  interrupted. 

The  current  may  be  more  or  less  shunted  or  diverted  from 
its  proper  path  by  the  accidental  establishment  of  other  paths, 
and  the  consequent  re-arrangement  of  the  current  distribution. 

The  generator  may  fail  entirely  to  develop  the  E.M.F.,  if, 
for  example,  the  field  coil  circuit  should  become  broken  and 
the  cores  thus  lose  their  magnetism. 

In  locating  a  fault  the  circuit  in  which  it  occurs  must  first 
be  determined,  and  then  the  various  points  at  which  it  might 
exist  must  be  examined,  one  after  another.  The  circuit  in  which 
the  fault  is  located  can  usually  be  inferred  from  the  extent  of  the 
disturbance.  If  only  a  single  light  goes  out,  it  is  evidently 
limited  to  the  circuit  belonging  that  light  alone,  and  may  be 
looked  for  in  the  lamp  itself  or  in  the  fuse  block,  if  it  has  one. 
If  all  the  lights  on  a  single  circuit  go  out,  but  no  others,  the 
trouble  is  of  course  limited  to  that  circuit,  and  may  probably  be 
found  at  the  junctions  with  the  main  feeders.  If,  on  the  con- 
trary, the  lights  in  all  of  the  circuits  go  out  or  fall  off  in  candle 
power,  the  trouble  is  in  the  main  circuit  and  must  be  sought  for 
at  the  switchboard  or  generator  itself.  At  the  switchboard 
the  cut  outs  and  fuses  must  be  examined,  and  if  the  trouble  is 
here  it  will  be  soon  located.  At  the  generator  the  brushes 
should  be  examined  to  make  sure  that  they  run  with  proper  con- 


58o  PRACTICAL  MARINE  ENGINEERING. 

tact  on  the  commutator.  The  contact  between  the  brush  and 
holder  and  all  binding  posts  and  contacts  about  the  machine 
should  also  be  examined,  in  order  to  make  sure  that  the  trouble 
is  not  in  a  poor  contact  at  these  points.  If  nothing  is  found 
here,  it  is  probable  that  the  fault  lies  in  the  armature  or  field 
coils,  and  that  possibly  they  have  become  burned  out  or  un- 
soldered or  otherwise  disconnected  at,  some  point. 

Leakage  faults  may  occur  where  the  insulation  is  partially 
or  wholly  destroyed,  and  the  result  of  such  leakage  will  be  a 
loss  of  effect  in  the  lighting  and  power  circuits.  Thus,  for  ex- 
ample, the  insulation  between  the  brush  carriers  and  the  base 
of  the  machine  may  become  faulty  by  wear  or  by  the  accumula- 
tion of  copper  dust  and  oil  and  thus  form  a  more  or  less  ready 
path  from  one  brush  to  the  other  through  the  base  of  the  ma- 
chine. In  such  case  the  current  traversing  both  the  field  coils 
and  external  circuit  will  be  cut  down,  and  due  to  the  former  the 
strength  of  the  magnetic  poles  will  be  diminished,  and  the 
E.M.F.  developed  will  fall  off  correspondingly.  In  case  these 
leakage  contacts  are  good,  the  entire  machine  will  shut  down, 
due  to  failure  of  current  in  the  magnet  coils  and  consequent 
failure  of  the  magnetic  field.  In  order  that  such  trouble  may 
exist,  both  brushes  must  be  thus  connected  to  the  base.  If  one 
only  is  connected,  the  machine  is  said  to  be  grounded.  No  imme- 
diate trouble  may  occur,  but  if  any  accidental  connection  is  set 
up  between  the  external  circuit  and  the  structure  of  the  ship 
the  leakage  circuit  will  be  complete  and  trouble  will  develop 
immediately,  its  character  and  extent  depending  on  what  point 
of  the  external  circuit  is  thus  grounded  with  the  machine. 

The  repair  of  a  fault  in  the  external  circuit  is  often  a  simple 
matter  of  cleaning  and  readjustment.  In  the  generator  itself, 
however,  the  exact  location  and  repair  of  a  fault  may  require  a 
complete  dismantling,  and  perhaps  a  partial  re-building  of  the 
machine. 


Practical  Marine  Engineering 

PART  II 


Practical  Marine  Engineering 

PART  II. 

COMPUTATIONS  FOR  ENGINEERS. 

Sec.  i.  COMMON  FRACTIONS.* 

[i]  Units  of  Measurement  and  Definitions. 

One  of  the  principal  duties  of  the  engineer  is  to  measure 
things.    Thus  he  may  be  called  on  to  find  the  length  of  a  sec- 
tion of  shafting,  the  diameter  of  a  piston-rod,  the  weight  o! 
a  screw-propeller,  the  volume  of  an  oil-tank,  or  the  capacity  of  a 
coal-bunker.     Measuring  consists  in  nothing  more  or  less  than 
comparing  the  quantity  to  be  measured  with  another  quantity 
of  the  same  kind,  and  so  finding  how  many  times  the  latter  is 
contained  in  the  former.     Thus  in  measuring  a  length  of  shaft 
with  a  foot  rule  we  really  compare  the  length  of  the  shaft  with 
the  length  of  the  rule,  and  so  find,  for  example,  that  the  shaft 
is  14  feet  in  length;  that  is,  that  it  is  14  times  as  long  as  the 
rule,  or  that  its  length  contains  the  length  of  the  rule  14  times. 
All  these  are  simply  different  ways  of  saying  the  same  thing. 
Now  the  foot  rule  or  the  foot  in  such  an  operation  is  called  the 
unit. 

Again,  in  measuring  the  weight,  say,  of  a  screw  propeller, 
the  operation  really  amounts  to  making  a  comparison  between 
the  weight  of  the  propeller  and  the  standard  weight  called  the 
pound.  Here  likewise  the  pound  is  the  unit. 

It  is  easily  seen  that  the  unit  must  be  the  same  kind  of 
quantity  as  the  thing  to  be  measured,  else  no  direct  comparison 
can  be  made  between  them :  thus  a  unit  length  to  measure 
length,  a  unit  area  to  'measure  surface,  a  unit  volume  to  measure 
volume,  a  unit  weight  to  measure  weight,  etc. 


*The  reader  is  supposed  to  he  somewhat  familiar  with  the  general  sub- 
ject of  fractions  as  presented  in  the  elementary  text  books  of  arithmetic. 
The  present  section  is  not  intended  as  a  complete  discussion  of  the  subject, 
but  rather  as  a  short  compendium  of  the  more  important  operations,  based 
on  a  point  of  view  somewhat  different  from  that  given  in  the  usual  text  books. 


582  PRACTICAL  MARINE  ENGINEERING. 

Now  if  we  wish  to  measure  the  length  of  our  section  of 
shafting  with  some  degree  of  accuracy  we  shall  probably  find 
that  it  is  not  an  exact  number  of  feet.  We  may  perhaps  find  its 
length  between  14  and  15  feet.  We  then  proceed  to  measure  the 
inches  and  find,  let  us  say,  14  feet  5  inches,  with  an  additional 
length  less  than  one  inch.  With  still  greater  accuracy  we  might 
go  on  and  find  perhaps  14  feet  5T7¥  inches  as  the  length  correct 
to  a  sixteenth.  Now  let  us  set  down  this  length  as  follows :  14 
feet,  5  inches,  7  sixteenths  inch.  It  is  easily  seen  that  if  the  foot 
is  a  unit  of  length  so  is  the  inch,  and  so  is  the  sixteenth-inch. 
Here  then  in  measuring  a  piece  of  shaft  we  have  used  three 
kinds  of  units,  the  foot  for  most  of  the  length,  the  inch  for  most 
of  the  remainder,  and  the  sixteenth-inch  for  the  little  that  finally 
remained.  We  know  very  well  that  the  sixteenth-inch  is  ob- 
tained by  simply  dividing  the  inch  up  into  sixteen  equal  parts 
and  taking  one  of  them,  while  the  inch  is  gotten  similarly  by 
dividing  the  foot  into  twelve  equal  parts  and  taking  one  of  them. 
It  thus  appears  that  these  units  are  all  related  together ;  the  six- 
teenth comes  from  the  inch,  and  the  inch  from  the  foot. 

A  unit  which  is  thus  obtained  by  taking  one  of  the  equal 
parts  into  which  a  larger  or  principal  unit  may  be  divided  is 
often  called  a  fractional  unit.  Thus  the  inch  is  a  fractional  unit 
relative  to  the  foot;  while  the  half-inch,  quarter-inch,  eighth- 
inch,  etc.,  are  all  fractional  units  relative  to  the  inch.  In  general 
we  can  always  suppose  any  given  quantity  considered  as  a  prin- 
cipal unit,  to  be  divided  up  into  any  number  of  equal  parts,  as 
3,  8,  16,  100,  144,  2196,  etc.,  and  wre  can  then  take  one  of  these 
parts  as  a  fractional  unit  and  with  it  proceed  to  measure  any 
given  amount  of  the  same  kind  of  quantity. 

Now  when  we  measure  quantities  with  fractional  units  the 
result  is  known  as  a  fraction.  Thus  the  fraction  five-twelfths  (^) 
is  the  measure  of  a  quantity  in  terms  of  the  unit  one-twelfth,  just 
as  five  inches  is  the  measure  of  a  quantity  in  terms  of  the  unit 
one  inch,  and  in  each  case  the  measure  is  simply  five  such  units. 
Or  to  put  the  same  thing  the  other  way  around,  if  we  measure  a 
quantity  in  terms  of  a  fractional  unit  such  as  one-twelfth  (TV), 
for  example,  and  find  that  the  measure  is  five  such  units,  then 
we  write  the  result  /V.  and  such  an  expression  is  known  as  a 
fraction.  For  the  engineer  it  is  always  most  natural  to  bear  in 
mind  this  idea  of  a  fraction,  and  to  consider  that  it  is  simply  the 
measure  of  a  certain  quantity  in  terms  of  a  fractional  unit. 


COMPUTATIONS  FOR  ENGINEERS.  583 

When  we  are  handling  fractions  simply  for  exercise  in 
arithmetic  we  do  not  always  stop  to  ask  what  kind  of  a  unit  it 
is,  or  what  kind  of  a  quantity  we  are  dealing  with.  For  an  ex- 
ercise in  arithmetic  it  makes  no  difference,  but  the  engineer  in 
actual  problems  always  knows  what  he  is  dealing  with,  and  what 
kind  of  a  unit  is  meant. 

In  the  usual  way  of  writing  fractions,  as  y\,  y^,  y\,  T\3T,  etc., 
the  number  below  the  line  is  called  the  denominator  and  shows 
into  how  many  equal  parts  the  larger  or  principal  unit  is  divided 
in  order  to  furnish  the  smaller  or  fractional  unit.  The  denomi- 
nator thus  shows  the  relation  of  the  fractional  unit  to  the  prin- 
cipal unit.  The  number  above  the  line  is  called  the  numerator 
and  shows  how  many  of  these  fractional  units  are  used  to  meas- 
ure the  quantity  in  question. 

PROPER  FRACTION.  In  a  proper  fraction  such  as  J  the  nu- 
merator is  less  than  the  denominator,  showing  that  the  quantity 
measured  is  less  than  the  principal  unit. 

IMPROPER  FRACTION.  In  an  improper  fraction  as  yf,  the 
numerator  is  greater  thanv  the  denominator,  showing  that  the 
quantity  measured  is  greater  than  the  principal  unit. 

MIXED  NUMBER,  OR  WHOLE  NUMBER  AND  FRACTION.  Such 
an  expression  means  that  the  quantity  is  measured  in  terms  of 
two  units.  Thus  7f\  means  seven  principal  units  and  five  frac- 
tional units,  the  latter  unit  being  one-twelfth  the  former.  This 
is  exactly  similar  to  the  measurement  of  length  in  feet  and 
inches,  or  weight  in  pounds  and  ounces.  Thus  if  the  foot  is  the 
principal  unit,  *j{\  means  simply  7  feet  and  5  inches,  or  if  the 
pound  is  the  principal  unit,  8-j^-  means  8  pounds  and  9  ounces. 
We  may  also  recall  the  illustration  used  near  the  beginning  of 
this  section  where  three  units  were  used  to  find  the  length  of  a 
piece  of  shafting. 

[2]  Reduction  of  a  Mixed  Number  to  an  Improper  Fraction. 

This  means  simply  the  reduction  of  the  measure  all  to 
terms  of  the  smaller  or  fractional  unit,  just  as  we  may  re- 
duce a  measure  in  feet  and  inches  all  to  inches.  Thus  to  reduce- 
7fV  to  an  improper  fraction  we  see  that  in  each  of  the  seven 
principal  units  there  are  12  fractional  units,  and  hence  7  X  12  or 
84  such  units  in  the  whole  number.  In  addition,  there  are  5 
more  fractional  units,  and  therefore  84  -)-  5  or  89  in  all.  The 
reduced  value  is  therefore  yf.  In  a  similar  way  if  the  principal 


584  PRACTICAL  MARINE  ENGINEERING. 

unit  were  the  foot  we  should  reduce  7  feet  and  5  inches  to  inches 
by  multiplying  the  7  by  12  and  adding  in  the  5,  giving  89  inches 
similar  to  the  89  twelfths  (ff)  above.  We  have  therefore  the 
following  : 

Rule.-^  Multiply  the  whole  number  by  the  denominator  and 
add  in  the  numerator.  The  result  is  the  numerator  of  the  im- 
proper fraction,  and  the  denominator  is  the  same  as  before. 

Problems  —  Reduce  to  improper  fractions  the  following  : 

I2|f,  1  7ff,  264-}-Jf. 


[3]  Reduction  of  an  Improper  Fraction  to  a  Mixed  Number. 

To  reduce  an  improper  fraction  such  as  fj-  to  a  mixed 
number  we  must  evidently  find  first  how  many  principal  units 
there  are.  Since  12  fractional  units  make  i  principal  unit,  it  is 
evident  that  the  number  of  principal  units  will  be  found  by 
dividing  31  by  12.  The  quotient  will  then  give  the  number  of 
principal  units  and  the  remainder  will  give  the  remaining  num- 
ber of  fractional  units.  Thus  31  -f-  12  =  2  principal  units  and 
7  remainder,  or  7  fractional  units  over;  or  f^  —  2TV  Hence 
the  following  : 

Rule  —  To  reduce  an  improper  fraction  to  a  mixed  number, 
divide  the  denominator  into  the  numerator  and  the  quotient  will 
be  the  whole  number,  while  the  remainder  will  be  the  numerator 
of  the  fraction,  and  the  denominator  will  be  as  before. 

Problems  —  Reduce  to  mixed  numbers  the  following  : 

76        198        289        56        95        143        2_6  4         764 
TJ>    T?¥>    TOT'     2T>    T6~>    TTT>      8?  »       T¥  • 


[4]  Reduction  of  Fractions  Without  Change  of  Value. 

If  we  change  the  size  of  a  unit  of  measure  we  shall 
change  the  measure  of  the  quantity  in  like  proportion.  Thus, 
for  example,  the  number  measuring  the  diameter  of  a  bolt  in 
sixteenths  as  a  unit  will  be  twice  as  great  as  if  measured  in 
eighths  as  a  unit.  Thus  T6g-  and  f  represent  the  same  quantity, 
one  measure  being  in  sixteenths  and  the  other  in  eighths.  It 
follows  that  we  can  multiply  or  divide  both  terms  of  a  fraction 
(the  numerator  and  denominator)  by  the  same  number  without 
changing  its  value.  Thus  f,  f,  f,  {%,  ^  if,  fj,  ff,  etc.,  all 
represent  the  same  quantity  measured  in  terms  of  different 
units,  and  it  is  seen  that  the  f  may  be  changed  into  any  of  the 
other  forms  by  multiplying  both  numerator  and  denominator 


COMPUTATIONS  FOR  ENGINEERS.  585 

by  the  same  number,  and  similarly  any  of  these  latter  forms 
may  be  reduced  back  to  the  f  by  dividing  both  numerator  and 
denominator  by  the  same  number. 

-7  «    A  and   'All*  «     . 


3X7  24-^- 

It  may  often  be  convenient  to  reduce  a  fraction  to  another 
of  equal  value  but  having  some  particular  or  specified  denomi- 
nator. To  this  end  we  divide  the  denominator  desired  by  the 
denominator  of  the  fraction,  and  multiply  both  terms  of  the 
fraction  by  the  quotient.  That  is,  we  must  multiply  both  nu- 
merator and  denominator  by  some  number  which  will  produce 
the  desired  denominator.  Thus  to  reduce  f  to  a  fraction  whose 
denominator  is  42  we  divide  42  by  3  and  find  14.  We  then  mul- 
tiply both  terms  of  f  by  14  and  thus  find  ff  as  the  fraction 
desired. 

LOWEST  TERMS.  A  fraction  is  said  to  be  reduced  to  its 
lowest  terms  where  there  is  no  whole  number  which  will  divide 
both  numerator  and  denominator  without  a  remainder.  Thus 
in  the  foregoing  string  of  fractions  f  is  in  its  lowest  terms  while 
none  of  the  others  is.  To  reduce  a  fraction  to  its  lowest  terms 
we  seek  a  factor  which  will  divide  both  numerator  and  denomi- 
nator and  divide,  continuing  the  operation  until  no  further  re- 
duction can  be  made. 

Example  —  Reduce  ^-f  to  its  lowest  terms.  We  may  first 
see  that  2  will  divide  both  terms  without  remainder.  Dividing 
we  have  r\  as  a  reduced  value.  We  then  see  that  3  will  again 
divide  both  terms,  and  thus  find  |  as  the  lowest  reduction.  We 
may  also  note  at  first  that  6  will  evenly  divide  both  terms,  and 
thus  find  J  by  a  single  operation. 

Problems  —  Reduce  the  following  to  their  lowest  terms  : 

*f».  W.  -ff#*  tf.  iWr,  K.  H>  tf 


ADDITION,   SUBTRACTION,    AND  MULTIPLICATION  OF 
COMMON   FRACTIONS. 

Considering  fractions  as  representing  the  measures  of  va- 
rious quantities,  we  may  be  called  upon  to  perform  upon  them 
the  fo'T  fundamental  operations  of  mathematics — addition,  sub- 
traction, multiplication,  and  division.  These  we  will  briefly 
consider  in  order. 


586  PRACTICAL  MARINE  ENGINEERING. 

[5]  Addition  of  Common  Fractions. 

We  cannot  combine  directly  f  and  f  into  a  single  quan- 
tity any  more  than  we  can  2  feeet  and  3  inches,  or  6  miles  and 
8  feet.  The  reason  is  that  the  units  are  not  the  same  in  the 
two  quantities  which  we  seek  to  combine,  and  before  the  com- 
bination can  be  effected  we  must  reduce  the  measures  to 
the  same  unit  in  each.  To  this  end  we  take  advantage 
of  the  operations  explained  in  [4]  and  reduce  the  frac- 
tions to  a  common  denominator  or  common  unit  of  meas- 
ure. We  naturally  seek  for  this  denominator  as '  small  a 
number  as  possible,  and  hence  proceed  according  to  the  com- 
mon rule  for  finding  the  L.  C.  M.  (least  common  multiple)  of  the 
denominators.  We  then  proceed  to  express  the  various  frac- 
tions all  with  this  L.  C.  M.  as  the  common  denominator  by  the 
method  explained  in  [4].  We  may  then  add  the  numerators 
and  reduce  the  result  as  may  be  possible.  This  is  the  foundation 
for  the  usual  rule,  which  may  be  expressed  as  follows : 

Rule,  (i)  Find  the  L.  C.  M.*  of  all  the  denominators  for  a 
new  denominator. 

(2)  Divide  each  denominator  into  this  L.  C.  M.  and 

multiply  the  corresponding  numerator  by  the 
quotient  for  a  new  numerator. 

(3)  Add  the  new  numerators  thus  found,  and  the  re- 

sult is  the  numerator  of  the  sum  desired. 

(4)  Write  this  numerator  over  the  L.  C.  M.  or  com- 

mon denominator,  and  reduce  to  the  lowest 
terms. 


*  For  convenience  in  connection  with  these  operations,  we  give  as  fol- 
lows the  rule  for  finding  the  least  common  multiple  of  a  series  of  numbers — 
*.  e.y  the  smallest  number  which  will  contain  each  without  a  remainder. 

Rule. — Write  the  numbers  in  a  line  (as  (i)  below),  and  select  any  num- 
ber (as  4  in  this  case)  which  will  divide  at  least  two  of  them  without  re- 
mainder. Divide  and  set  down  the  quotients  underneath,  except  where  the 
division  would  not  be  exact,  in  which  case  bring  down  agnin  the  number 
itself  (as  shown  in  line  (2)  below).  Proceed  with  this  line  the  same  as  with 
the  first,  and  so  continue  until  no  two  numbers  have  a  common  divisor. 
Then  multiply  together  all  the  numbers  remaining  on  the  last  line,  together 
with  all  the  divisors,  and  the  product  will  give  the  least  common  multiple 
desired. 

Example.—  Find  the  L.  C.  M.  of  8,  36,  20,  6. 
Operation: — 

4)  8        36        20        6. . .  .Line  (i) 

3)  2          9          56 Line  (2) 

2)  2          352 Line  (3) 

i          3          5         i Line  (4) 

L.  C.  M.=4XX2XX=6°-— Ans- 


COMPUTATIONS  FOR  ENGINEERS.  587 

Examples.    Add  -^  and  {. 

The  L.  C.  M.  of  18  and  4  is  36.    We  then  have : 

5       4-     1     -    T  °   +   9   _    !  9 
1  x         '     4    ~       "Tfc ~  f*' 

Add  YV,  *  and  f 

The  L.  C.  M.  of  16,  3  and  6  is  48.    We  then  have : 

-fg  4-  f  4-  f  — —  =  -f-J-  =  by  reduction  -J^-. 

If  there  are  but  two  fractions  to  be  added  and  both  have  i 
for  a  numerator,  a  short  rule  for  their  addition  is  as  follows : 
Write  the  sum  of  the  denominators  over  their  product  and  the 
fraction  thus  formed  is  the  sum  desired. 

Thus  i  4-  i  =  if  -  T7T. 

[6]  Subtraction  of  Fractions. 

This  operation  requires  reduction  to  the  same  unit  of  meas- 
ure in  the  same  way  and  for  the  same  reason  as  in  the  case  of 
addition.  We  have  hence  the  usual  rule,  which  may  be  expressed 
as  follows : 

(1)  Find  the  L.  C.  M.  of  the  two  denominators  for  a  new 
denominator. 

(2)  Divide  each  denominator  into  this  L.  G.  M.  and  mul- 
tiply the  corresponding  numerator  by  the  quotient  for  a  new 
numerator. 

(3)  Subtract  the  new  numerators,  and  the  result  will  be 
the  numerator  of  the  difference  desired. 

(4)  Write  this  numerator  over  the  L.  C.  M.  or  common 
denominator,  and  reduce  to  lowest  terms.     Thus  to  subtract 
%  from  T7ff  we  have  as  follows  : 

_7      _  i  =     T4  —  9  _ 

36 

If  both  numerators  are  i  a  short  rule  for  the  subtraction 
of  the  fractions  is  as  follows  :    Write  the  difference  of  the  de- 
nominators over  their  product  and  the  fraction  thus  formed  is 
the  difference  desired. 
Thus  i  —  4-  =  TV 

Problems  in  Addition  and  Subtraction  of  Fractions.  Perform 
the  following  additions : 

(1  +  i  + 1),  (t  +  f  +  TV).  (¥  +  I),  (*  +  it),  (W  +  A)- 

Perform  the  following  subtractions : 

/3_.     1\       (M  1   \      /814  13\      /430  10  4\      /17          "1\ 

(i      TT/I  VTI        T*/>  (TTT  ~~  TT;»  vtti     ~  Tirf/»  UT  —  T-) 


588  PRACTICAL  MARINE  ENGINEERING. 

Note. — In  the  operation  of  multiplication  and  division  we 
should  always  distinguish  between  the  operator  and  the  subject  or 
thing  operated  on.  Thus  in  6  times  5,  the  number  6  is  the  operator 
and  5  is  the  subject.  The  latter  is  usually  the  measure  of  some 
quantity.  The  former  is  the  sign  of  an  operation  to  be  per- 
formed, and  this  distinction,  which  is  most  important,  must  not 
be  forgotten. 

[7]   Multiplication  of  Fractions. 

We  shall  first  consider  the  operator  as  a  whole  number  and 
the  subject  as  a  fraction.  Thus  suppose  that  we  wish  to  multiply 
-£%  by  6.  The  operation  is  exactly  the  same  as  if  we  wished  to  mul- 
tiply 5  inches  by  6.  The  result  in  the  latter  case  is  30  inches  and  in 
the  former  it  is  30  twelfths,  or  as  we  may  write  it:  f§,  or  by 
reduction  f,  or  2^.  This  illustrates  the  familiar  principle  that 
to  multiply  a  quantity  we  must  multiply  its  measure,  and  since 
in  a  fraction  the  numerator  is  the  measure,  we  multiply  the 
numerator  to  multiply  the  fraction. 

Furthermore,  it  is  plain  if  we  multiply  the  denominator  of 
a  fraction  that  we  'decrease  the  size  of  the  fractional  unit,  and 
hence  with  the  same  numerator  or  same  number  of  such  units 
we  'decrease  the  value  of  the  fraction  in  like  proportion.  Simi- 
larly if  we  'divide  the  denominator  we  increase  the  size  of  the 
fractional  unit,  and  hence  with  the  same  numerator  or  same 
number  of  such  units  we  increase  the  value  of  the  fraction  in 
like  proportion.  Hence  if  we  can  divide  the  denominator  of 
the  fraction  by  the  given  multiplier  and  leave  the  numerator 
the  same,  it  will  have  the  same  effect  as  multiplying  the  nu- 
merator and  leaving  the  denominator  the  same.  Thus  -^  X 

3=  \-_ 

This  may  also  be  seen  by  first  multiplying  the  numerator 
and  then  reducing  to  lowest  terms.  Thus  ^  X  3  =  -fr  = 
by  reduction  \.  Hence  we  have  the  following  rule  for  multi- 
plying by  a  whole  number : 

Rule — Multiply  the  numerator  of  the  fraction  or  divide  the 
denominator  of  the  fraction  by  the  given  number. 

Problems — Perform  the  following  multiplications  : 
f  X  2,  f  X  3,  A  *  4,  TV  X  6,  -If  X  7,  fi  X   12,  ^V  x  3^- 


[8]  Divisions  of  Fractions. 

As  before,  we  first  consider  the  divisor  or  operator  as  a  whole 
number,  and  the  dividend  or  subject  as  a  fraction.    Then  we  may 


COMPUTATIONS  FOR  ENGINEERS.  589 

remember  that  division  is  simply  the  inverse  of  multiplication, 
and  that  by  inverting  the  procedure  for  the  latter  we  shall  effect 
the  former.  Thus  to  divide  -J-f  by  2  we  divide  18  by  2  and  have  -^ 
as  the  result.  Or  again  we  may  multiply  the  denominator,  thus 
dividing  the  value  of  the  fractional  unit  and  thus  dividing  the 
value  of  the  fraction  as  explained  in  [7].  Thus  -^f  -r-  2  =  ££. 
This  being  reduced  to  its  lowest  terms  gives  •£$  as  before. 

The  operations  on  fractions  involved  in  multiplication  and 
division  by  whole  numbers  may  be  summarized  as  follows : 

n,   «, .   1    .         ,,       f  numerator      ")  (  multiplies ) 

Multiplying  the  { denominator }         (divides       }       lts 

j    j.    .  -,.  (  numerator      |  (  divides       ) 

value,  and  dividing  the     ]  denominator  [        {multiplies} 

its  value. 

Problems — Perform  the  following  divisions : 

f  -  4, 1  -  3,  A  -*-  *,  «  •*-  7,  M  -+-  4,  ¥  -  3,  Hi  -*-  ii. 

[9]  Multiplication  and  Division  by  Fractions. 

In  these  operations  the  operator  is  expressed  as  a  fraction, 
and  the  latter  in  this  case  is  therefore  not  the  measure  of  a  quan- 
tity, but  the  sign  of  something  to  be  performed.  When  the  frac- 
tion is  used  as  a  multiplier  it  is  simply  a  short-hand  way  of  ex- 
pressing two  operations  (i)  a  multiplication  by  the  numerator 
and  (2)  a  division  by  the  denominator.  Thus  if  •§•  is  used  as  a  mul- 
tiplier it  is  simply  a  short-hand  way  of  expressing  a  multiplica- 
tion by  2  and  a  division  by  3.  Thus  8  X  I  is  another  way  of 
expressing  8X2-^3  or  8-^-3X2. 

Similarly  and  since  division  is  exactly  the  inverse  of  mul- 
tiplication, when  a  fraction  is  used  as  a  divisor  it  is  simply  a 
short-hand  way  of  expressing  two  operations :  (i)  a  division  by 
the  numerator,  and  (2)  a  multiplication  by  the  denominator. 
Thus  if  f  is  used  as  a  divisor  it  is  simply  a  short-hand  way  of 
expressing  a  division  by  2  and  a  multiplication  by  3.  Thus  8 
-r-  |  is  another  way  of  expressing  8-^2X3  or  8X3-^-  2. 

When  the  thing  operated  on  is  also  a  fraction  these  prin- 
ciples work  out  as  follows :  5  X  i  means  that  f  is  to  be  multi- 
plied by  2  and  divided  by  5.  But  we  can  multiply  by  multiplying 
the  numerator,  and  we  can  divide  by  multiplying  the  denomina- 
tor. Hence 

3.  x  f  =  ^ =  -£$  =  j\.       Hence   for   the    multiplication  of 

4  x  5 


590  PRACTICAL  MARINE  ENGINEERING. 

one  fraction   by  another  we  have  the  usual  rule  as  follows : 
Rule — Multiply  together   the   two   numerators   for   a   new 
numerator  and  the  two  denominators  for  a  new  denominator, 
and  the  fraction  thus  formed  is  the  product  desired. 

Similarly  for  division,  f  -r-  -f-  means  that  f  is  to  be  divided 
by  2  and  multiplied  by  5.  But  this  is  the  same  as  the  pair  of 
operations  expressed  by  using  4  as  a  multiplier.  Hence 

t  -  1  =   f   X   f  =   ¥;  . 

Hence  for  the  division  of  one  fraction  by  another  we  have 
the  usual  rule  as  follows : 

Rule — Invert  the  terms  of  the  divisor  and  proceed  as  in 
multiplication. 

This  might  naturally  be  expected  by  remembering  the.  rela- 
tion between  multiplication  and  division,  and  that  one  is  the 
exact  inverse  of  the  other. 

For  the  multiplication  of  a  series  of  fractions  into  each 
other  these  principles  work  out  as  follows :  If  X  £  X  f  X  i 
means  that  -J  is  first  considered  as  a  subject  and  f  as  an  opera- 
tor. Then  the  result  of  this  is  the  subject  and  f  is  the  operator 

1X3X2X5 

and  so  on.    The  final  result  will  be  therefore 

2  X  5  <X  /  X  9 

=-££$.  In  this  result  we  have  a  numerator  30  whose  factors 
are  the  numerators  of  the  individual  fractions,  while  similarly 
the  denominator  630  has  for  its  factors  the  individual  denomi- 
nators. Applying  here  the  principles  of  [4]  we  may  cross  out 
from  numerator  and  denominator  any  pair  of  common  factors. 
This  will  shorten  the  operation  and  give  the  result  in  its  lowest 
terms.  Thus  shortened  the  above  case  becomes : 

1        X       ff       X       2       X       ft     _       j_ 

£     x     0     x     7     x    ~0  ""  21 
3 

The  propriety  of  striking  out  a  common  factor  in  both  nu- 
merator and  denominator  may  also  be  seen  by  remembering 
that  such  a  pair  of  factors  denote,  one  a  multiplication  and  the 
other  a  division  by  the  same  number.  These  operations  will 
offset  each  other  and  may  therefore  be  omitted  entirely. 

CANCELLATION.  This  striking  out  of  common  factors  from 
both  terms  of  a  fraction  is  known  as  cancellation,  and  is  often  of 
great  value  in  simplifying  an  operation  before  proceeding  with 


COMPUTATIONS  FOR  ENGINEERS.  591 

the  actual  multiplication  and  division.     The  following  are  addi- 
tional illustrations. 


_ 

X 


7         2 

21  22  #X?0X?;xffil          I4 


33        42         8  8  -  ^  x  ffl  x    $  x  #-   27 

73        3  9 

_±  ,  .  J5  x  J  6      £Z  _    4  x  #  x  ;0  x  ffl  _  -i_ 

81     16     60     2  -     x     X     x  2  "  6 


2    ^     "2    ^     T  6 

We  often  meet  with  expressions  like  —     „     —      in  which 

9X8 

the  number  of  factors  in  numerator  and  denominator  is  not 
the  same.  All  such  expressions  represent  a  series  of  multipli- 
cations of  whole  numbers  and  fractions  as  f  X  f  X  16,  or  they 
may  be  considered  as  denoting  a  series  of  operations  of  mul- 
tiplication and  division,  and  in  either  case  it  follows  that  their 
reduction  may  be  effected  by  cancellation  as  just  described. 
Still  otherwise  we  may  consider  such  expressions  as  consisting 
of  a  numerator  and  denominator  each  resolved  into  factors, 
and  hence  in  ready  condition  for  reduction  by  cancellation. 
Thus  in  the  expression  above  we  have  : 


PX'J5  3 

3 
Problems — Perform  the  following  operations : 

(I  X    «),   (f  X  I),    (s    x  ||),   (JV  X  f  X   I),   (T<y  X  J/  X   i), 

(2     X     f     X     2/). 

(¥  +  I),  (¥  *  IV  (T¥T  -  «),  (II  *  A)  (A  t  TV),  (I  +  ¥)- 

[10]  Complex  Fractions. 

In  complex  fractions  either  or  both  numerator  and  denomi- 
nator may  consist  of  fractions  or  mixed  numbers. 

Thus  for  example :  ~p  -i'  — 
5      f    3i  ' 

All  such  expressions  may  most  conveniently  be  considered 
as  ways  of  indicating  operations,  the  numerator  being  the  sub- 
ject of  the  operation  and  the  denominator  being  the  operator 
expressed  as  a  divisor. 


592  PRACTICAL  MARINE  ENGINEERING. 

• 

Thus 

4  =  *i * i  =  *•*•  f  =  f  x  |  =  y. 

5 

~   4  ^  £  —   •!•   X    3-  ==   -1- 

7" 

*?i  5  O5  5  o  5         '      1  6  8* 

The  reduction  of  such  expressions  becomes  therefore 
simply  a  matter  of  the  application  of  the  rules  and  methods 
already  given. 

Problems — Reduce  the  following: 

8|T'  i  -  6.  x  |  '       2-|  X  I  -   if    ' 

Sec.  2.     DECIMAL  FRACTIONS. 

[i]  In  decimal  fractions  the  denominator  is  always  10,  100, 
1000,  etc.,  or  some  power  of  10.  Instead  of  writing  them  in 
the  usual  way,  however,  a  device  is  made  use  of  to  indicate  the 
denominator  without  actually  writing  it.  This  is  simply  to  write 
the  numerator  and  to  place  a  dot  at  such  a  point  that  there  shall 
be  as  many  figures  on  the  right  as  there  are  ciphers  in  the  de- 
nominator, using  ciphers  to  the  left  of  the  significant  figures  if 
necessary  to  make  up  the  needed  number  of  places.  In  writing 
a  mixed  number  the  whole  number  part  stands  on  the  left  of  the 
dat  or  decimal  point,  which  thus  becomes  a  point  of  separation 
between  the  whole  number  and  the  fraction. 

Thus 


Y7^  is  written         .7 

TUTF 

" 

.07 

7         <  i 

•eruiT 

<  i 

.007 

23          « 

1  1 

.0023 

2T7~0~    " 

<  < 

2.7 

fro   " 

<  i 

162.043 

In  each  case  it  is  seen  in  the  decimal  that  there  are  as  many 
places  on  the  right  of  the  dot  as  there  are  ciphers  in  the  de- 
nominator, and  in  this  way  the  value  of  the  denominator  or 
unit  of  measure  is  indicated.  There  are  no  principles  involved 
in  decimal  fractions  different  from  those  already  discussed  in 
common  fractions,  and  the  only  difficulties  in  using  them  arise 
irom  the  peculiar  manner  in  which  they  are  written.  We  will 
therefore  give  without  further  discussion  the  rules  for  the 


COMPUTATIONS  FOR  ENGINEERS.  593 

handling  of  decimals,  all  of  which  may  be  seen  to  follow  from 
the  principles  already  laid  down. 

[2]  To  Reduce  Decimals  to  I/ower  Terms. 

Evidently  all  ciphers  standing  on  the  right  of  the  decimal 
may  be  struck  off  as  they  disappear  from  both  numerator  and 
denominator.  Thus  .3500  =  .35. 

[3]  To  Raise  Decimals  to  Higher  Terms. 

Add  ciphers  to  the  right  of  the  numerator  as  may  be  de- 
sired. Thus  .35  =  .350  =  .3500. 

[4]  To  Reduce  a  Decimal  Fraction  to  a  Common  Fraction. 

Write  the  numerator  and  denominator  as  in  common  frac- 
tions and  reduce  to  lower  terms  if  possible. 

Example  —  Reduce  .35  to  a  common  fraction. 
Operation:    .35   =  ^  =  ^. 

[5]    To  Reduce  a  Common  Fraction,  Proper  or  Improper   to  a 

Decimal. 

Take  the  numerator  for  the  dividend  and  the  denominator 
for  the  divisor  and  proceed  as  in  division  of  whole  numbers,  add- 
ing ciphers  to  the  right  of  the  dividend  as  may  be  necessary. 
Then  point  off  according  to  the  following  rule  : 

If  the  numerator  or  dividend  is  less  than  the  denominator 
or  divisor,  the  first  figure  of  the  quotient  must  stand  on  the 
right  of  the  decimal  point  as  many  places  as  the  number  of 
ciphers  added  to  the  right  of  the  dividend  in  order  to  enable  it 
to  contain  the  divisor.  If  the  dividend  is  greater  than  the 
divisor  place  the  point  after  the  figure  of  the  quotient  given 
by  bringing  down  the  last  figure  of  the  dividend  in  the  opera- 
tion of  division. 

It  should  be  noted  that  this  gives  the  general  method  for 
dividing  one  whole  number  by  another  and  expressing  the  re- 
sult decimally. 

Examples  —  Reduce  ^W  to  a  decimal. 


Operation:  250")   1600   (.064 

1500 


IOOO 
1000 


Two  ciphers  are  annexed  in  order  to  obtain  the  first  figure 
6  in  the  quotient.     Hence  this  figure  must  stand  in  the  second 


594  PRACTICAL  MARINE  ENGINEERING. 

place  to  the  right  of  the  decimal  point,  and  a  cipher  is  added  on 
the  left  of  the  6  to  bring  it  to  this  position. 
Reduce   iff1  to  a  decimal. 

Operation:  25\   1647  (6588  220 

150  200 


147  200 

125  200 


The  figure  5  of  the  quotient  is  given  by  bringing  down  the 
last  figure  7  of  the  dividend,  and  hence  the  decimal  point  must 
come  between  this  and  the  next  figure  of  the  quotient. 

Problems  —  Reduce  the  following  to  decimals  : 

i  V*   H1,  WV,  itfr,  V,  W>  tttt,  Tttir.  T«IF.  V- 


[6]  To  Add  Decimals. 

Set  down  the  decimals  in  a  column  so  that  the  points  shall 
all  stand  under  each  other.  Then  add  as  in  whole  numbers  and 
bring  down  the  decimal  point  in  the  sum  under  thosev  standing 
above. 

Example  —  Add  .025,  .64,  .231,  .4685,  .003. 

Operation  :* 

.025 

.64 
.231 

4685 
.003 


1.3675 

[7]  To  Subtract  Decimals. 

Set  down  the  subtrahend  under  the  minuend,  the  two  deci- 
mal points  one  under  the  other,  adding  ciphers  to  the  right  if 
necessary  to  fill  out  to  the  same  number  of  places.  Then  sub- 
tract as  in  whole  numbers  and  bring  down  the  decimal  point  qn- 
der  those  above. 


*  If  desired,  the  numbers  may  be  filled  out  all  to  the  same  number  of 
places,  by  adding  ciphers  on  the  right,  such  operation  being,  in  fact,  the 
reduction  of  the  decimals  all  to  the  same  denominator  or  unit  of  measure. 
In  the  summing,  however,  such  ciphers  play  no  part,  and  therefore  the 
filling  out  is  unnecessary  in  the  actual  operation. 


COMPUTATIONS  FOR  ENGINEERS.  595 

Example — Subtract  .263  from  .83. 
Operation : 

.830 

.263 


.567 

18]  To  Multiply  Together  Two  Numbers  Expressed  Decimally. 

Multiply  as  in  whole  numbers  and  point  off  for  the  decimal 
portion  as  many  places  as  there  are  in  the  two  factors  taken 
together. 

Examples — 


16 

X 

24 

= 

3-84 

72. 

X 

.OOO4    =: 

.0288 

. 

162 

X 

.O4I       = 

.006642 

21. 

14 

X 

13 

= 

274.82 

21. 

H 

X 

•13          = 

2.7482 

21. 

H 

X 

I 

•3         = 

27.482 

Problems — Perform  the  following  multiplications  : 

2.72  X  14 

143.26  X  24.2 

12.16  X  -018 

4214.3     X  22.3 

.14  X  .21 

.06  X  .0084 

[9]  To  Find  the  Quotient  of  Two  Quantities  Expressed 
Decimally. 

Clear  both  dividend  and  divisor  of  decimals  by  moving"  the 
point  to  the  right  an  equal  number  of  places  in  each,  adding 
ciphers  as  may  be  necessary.  The  number  of  places  moved 
will  be  that  necessary  to  clear  the  term  of  higher  order.  Thus 
modified,  consider  the  two  terms  as  whole  numbers  and  proceed 
with  the  division,  pointing  off  according  to  the  rule  given  above 
for  the  reduction  of  a  common  fraction  to  a  decimal. 

Examples — 

.16       -5-     2.5       or  "J     =         jfo  =         .064 
1.6       -5-     2.5       or  II-   =  ft  =         .64 


596  PRACTICAL  MARINE  ENGINEERING. 

1.6       -       .25     or          =         Jfli  =         6.4 


16.         -5-       .025  or-   -  =     -uy^.  =  640. 


.016  -*•     250      or1^   2irUin>  =         .000064 
1.6     -*-     .243     <*~m       W  =       6.5761  4- 


Problems  —  Perform  the  following  divisions  : 

7.25         -  16 
72.54        —     6.4 
.00864  —       .14400 


8.64 

.96 

1.25 


.0144 

.024 

.0025 


Sec.  3.  PERCENTAGE. 

[i]  In  percentage,  fractional  reations  are  expressed  deci- 
mally, but  it  is  understood  that  the  denominator  shall  always 
be  100.  The  fractional  unit  is  therefore  always  one  one-hun- 
dredth of  the  principal  unit,  and  therefore  occupies  to  it  the 
same  relation  as  that  of  the  cent  to  the  dollar.  The  words  per 
cent  are  commonly  represented  by  the  symbol  %,  so  that  16% 
is  the  same  as  16  per  cent  or  .16,  while  5%  equals  similarly  .05, 
etc.  Care  must  be  had  not  to  fall  into  confusion  with  the  use 
of  both  the  decimal  point  and  %  mark.  Thus  .4%  is  not  .4, 
but  .4  of  one  per  cent  or  .004.  A  number  written  in  percentage 
is  usually  an  operator,  and  not  a  quantity  or  measure  by  itself. 
Thus  16%  is  not  a  quantity  by  itself,  but  rather  expresses  the 
relation  between  two  quantities,  or  represents  an  operation  to- 
be  performed  on  one  quantity  in  order  to  obtain  another.  The 
handling  of  percentages  is  the  same  as  that  of  decimals,  re- 
membering that  the  term  per  cent  is  simply  a  special  name  for 
a  fractional  unit  one  one-hundredth  of  the  principal  unit,  what- 
ever the  latter  may  be,  and  that  it  is  with  this  fractional  unit 
that  all  quantities  are  measured  in  percentage  operations.  Re- 
membering the  rules  for  decimals  we  readily  see  the  following : 


COMPUTATIONS  FOR  ENGINEERS.  597 

Examples  — 

i6foof8o    =80     X.  16=12.8 

3%  of   2.1  =    2.1  X  .03  =      .063 
23%  of  $145.24  =  $i45-24  X  .23  =  $33.4052,  or  $3341- 
From  the  above  it  follows  that  : 

To  reduce  any  number  expressed  in  per  cent  to  terms  of 
decimals,  we  divide  by  100  and  express  the  result  decimally,  or 
shift  the  decimal  point  two  places  to  the  left;  while  to  reduce 
any  decimal  to  terms  of  per  cent  we  multiply  by  100  or  shift  the 
decimal  point  two  places  to  the  right. 

Thus:  .16     =    16.% 

i  .60     =  160.% 
.016    =      1.6% 
.0016=       .16% 

To  FIND  THE  PERCENTAGE  RATIO  BETWEEN  Two 
NUMBERS. 

Rule  —  Multiply  the  dividend  or  numerator  by  100  and  then 
divide  and  express  the  result  as  a  decimal  according  to  the  rules 
of  Section  2  [9]. 

Thus:  7  -5-  25  or  fa  =  ^%  =  28%. 
Similarly  : 

3      -     5o    or     A  =         6% 


7      -*•     16    <>r  =       43-75 

6.4    -5-  160    or  —  '•—  =        4% 

TOO 

6.4-5-     1  6    or  —  ^-   =       40% 

19 

6.4  -T-  1.6     or  —  '—  =     400% 
i  .6 

6.4  -T-     .16  or  —  '—   =  4000% 

.  ID 

In  percentage  problems  it  is  usually  required  to  find  certain 
percentages  of  various  quantities,  or  to  find  the  percentage  re- 
lations between  various  quantities.  The  only  difficulty  likely  to 
arise  is  not  with  the  operations  themselves,  but  with  a  correct 
interpretation  of  the  problem  and  a  clear  understanding  as  to 
the  relations  desired. 


598  PRACTICAL  MARINE  ENGINEERING. 

Examples — 

(1)  A  broker  buys  a  ship  for  $160,000  and  sells  her  for 
$172,000.    What  per  cent  does  he  gain? 

Solution :  The  amount  of  gain  is  $12,000.  To  find  what  per 
cent  this  is  of  $160,000  we  proceed  as  above  and  find  12,000  -±- 
160,000=  ?.$%. 

(2)  A  broker  buys  a  ship  for  $160,000  and  sells  her  so  as  to 
gain  6%.    What  was  the  selling  price  ? 

Solution :  Six  per  cent  of  $160,000  =  .06  X  $160,000  = 
$9,600.  Hence  selling  price  =  $160,000  +  $9,600  =  $169,600, 

(3)  A  broker  sells  a1,  ship  for  $171,200  and  thereby  gains  7% 
on  her  cost.    What  was  the  cost  ? 

Solution :  Since  he  gains  7%  or  7  cents  on  every  dollar  of 
cost,  there  will  be  $1.07  in  the  selling  price  for  every  $1.00  in  the 
cost  price.  Hence  the  cost  price  will  be  as  many  dollars  as  1.07 
is  contained  in  171,200  or  160,000. 

Problems — 

(4)  Thirty-six  pounds  of  gun  metal  contain  the  following : 

Copper 32  pounds 

Tin i  pound 

Zinc  3  pounds 

Find  the  percentage  composition. 

Ans.         Copper f|  or  88 . 89% 

Tin -jV  or     2.78% 

Zinc -£$  or     8.33% 

(5)  A  ship  starts  on  a  voyage  of  2,200  miles.    After  going 
800  miles  what  per  cent  of  the  voyage  remains  to  be.  covered  ? 

Ans.  63.6%. 

(6)  A  ship  starts  on  a  voyage  of  1,800  miles.    After  three 
days  she  has  made  42%  of  the  distance.    With  12%  increase  of 
speed  for  the  rest  of  the  time  how  long  will  it  take  her  to  finish 
the  voyage  ? 

Ans.  6.3754  days. 

(7)  A  marine  engine  requires  2.1  Ibs.  of  coal  per  I.  H.  P. 
per  hour.    After  certain  changes  are  made  the  figure  is  reduced 
to  1.89  Ibs.    What  is  the  percentage  gain? 

Ans.  10%. 

In  one  ton  of  coal  (2,240  Ibs.)  there  was  found  to  be  250  Ibs. 
of  ashes.    What  per  cent  of  the  coal  was  combustible? 
Ans.  88.8%. 


COMPUTATIONS  FOR  ENGINEERS. 


599 


Sec.  4.     COMPOUND  NUMBERS. 

WEIGHTS  AND   MEASURES. 
[i]  IfOng  or  I/inear  Measure. 


Inches. 

Feet. 

Yards. 

Rods. 

Furlongs. 

Miles. 

Meters. 

i 

•0833 

.0278 

.00505 

.000126 

.000*016 

.0254 

12 

=i 

•333 

.0606 

.00152 

.000189 

•  305 

36 

3 

.182 

•00455 

.000568 

.914 

198 

i6# 

S*/* 

=i 

.025 

.00313 

5.029 

7920 

660 

220 

40 

•125 

201.166 

63360 

5-280 

1760 

320 

8 

=i 

1609.3 

39-371 

3.281 

1.094 

.199 

.00497 

.000621 

=  i 

SPECIAL  MEASURES. 

6        feet  =  i  fathom. 

120        fathoms  =  i  cable's  length. 

6080.27  feet  =  i  nautical  mile  (United  States). 

6080        feet  =  i  nautical  mile  (British). 

3        nautical  miles  =  i  marine  league. 


[a]  Avoirdupois  Weight  or  Measure. 


Tons. 

Drams. 

Ounces. 

Pounds. 

Long  or 

Short  or 

Kilos. 

British. 

Legal. 

i 

0621 

OO^Q 

16 

—  j 

062^ 

.02835 

256 

16 

=    I 

.000446 

.0005 

.4536 

573440 

35840 

2240 

—  i 

1.  12 

1016 

512000 

32000 

2uOO 

.89 

=  I 

907 

564-38 

35-27 

2  .  2046 

.000984 

.OOI  IO2 

=  i 

[3]  Square  Measure, 


Square 
Inches. 

Square 
Feet. 

Square 
Yards. 

Square 
Meters. 

i 

.00694 

.000772 

.000645 

144 

=  i 

.IIH 

.0929 

1296 

9 

=  i 

.8360 

i55o 

10.765 

1.196 

=  i 

6oo 


PRACTICAL  MARINE  ENGINEERING. 
[4]  Cubic  or  Volume  Measure. 


Cubic 
Inches. 

Cubic 
Feet. 

Cubic 
Yards. 

Cubic 
Meters. 

i 

0005788 

1728 
46656 
61033 

=  i 
27 
35-32 

•037 
=  i 
1.308 

.0283 

.7645 

=  i 

[5]  I/iquid  Measure. 


Cubic 
Inches. 

Gills. 

Pints. 

Quarts. 

Gallons. 

Barrels. 

U.S. 

British. 

8.665 
34-659 
69.318 
231 
277.274 

•"54 
=  i 

4 
8 
32 

32 
1008     , 

.02885 
•25 
=i 

2 

8 
8 
252 

.0144 
.125 

•50 
=  i 

4 
4 
126 

•00433 
.03125 
•125 

•  25 
=  i 

1.2 

31/2 

.00361 
.3125 
.125 
•25 
•833 

3I# 

.003175 
.003175 
=  i 

[6]  Dry  Measure. 


Cubic  Inches. 

Pints. 

Quarts. 

Pecks. 

Bushels. 

i 
33-6 
67.2 
537-6 
2150.42 

.02976 
=  i 

2 

16 
64 

.01488 
•5 

8 
32 

.00186 
.0625 
.125 

4 

.0004641 
.01^625 
•03125 
•25 

[7]  Shipping  Measure. 

i  register  ton                            =      mo       cubic  feet, 
i  United  States  shipping  ton  =  \    ^  u^d^es  bushels, 
i  British  shipping  ton              =   j    4^  fmp^riafbushels. 

[8]    The  Metric  System  of  Weights  and  Measures. 

MEASURES  OF  LENGTH. 


10  millimeters  (mm) 

10  ctntimeters 

10  decimeters 

10  meters 

10  dekameters 

10  hektometers. . 


=  i  centimeter. cm. 

=  i  decimeter  dm. 

=  i  meter m. 

=  i  drkameter Dm. 

=  i  hektometer Hm. 

=  i  kilometer. .  ...  Km. 


COMPUTATIONS  FOR  ENGINEERS. 


601 


MEASURES  OF  SURFACE  (Nox  LAND). 

100  square  millimeters  (mm2). .  —  i  square  centimeter  . .  .cm2. 

100  square  centimeters =  i  square  {decimeter.  ...dm2. 

100  square  decimeters =  i  square  meter m2. 

MEASURES  OF  VOLUME. 

1000  cubic  millimeters  (mm3). . .  =  i  cubic  centimeter cm3. 

1000  cubic  centimeters —  i  cubic  decimeter dm3. 

1000  cubic  decimeters =  i  cubic  meter m3. 


MEASURES  OF  CAPACITY. 


10  milliliters  (ml). 

10  centiliters 

10  deciliters 

10  liters 

10  dekaliters 

10  hektoliters. . 


centiliter cl. 

deciliter dl. 

liter 1. 

dekaliter.... .....Dl. 

hektoliter HI. 

kiloliter . .  . .  Kl. 


NOTE. — The  liter  is  equal  to  the  volume  occupied  by  i 
cubic  decimeter  of  pure  distilled  water  at  its  temperature  of 
maximum  density,  or  39.2°  F. 


MEASURES  OF  WEIGHT. 


10  milligrams  (mg). 

10  centigrams 

10  decigrams 

10  grams 

10  dekagrams 

10  hektograms 

1000  kilograms 


centigram eg. 

decigram dg. 

gram g. 

dekagram Dg. 

hektogram. ...... Hg. 

kilogram Kg. 

ton..  ..T. 


NOTE. — The  gram  is  the  weight  of  i  cubic  centimeter  of 
pure  distilled  water  at  a  temperature  of  39.2°  F. ;  the  kilogram 
is  the  weight  of  i  liter  of  water;  the  ton  is  the  weight  of  i 
cubic  meter  of  water. 


[9]    Conversion  Tables. 

ENGLISH  MEASURES  INTO  METRIC. 


English. 

Inches  to 
Millimeters. 

Feet  to 
Meters. 

Pounds  to 
Kilos. 

Gallons  to 
Liters. 

i 

25.4001 

.304801 

•45359 

3-78544 

2 

50.8001 

.609601 

.90719 

7.57o88 

3 

76.2002 

.914402 

1.36078 

ii.35<>32 

4 

101  .6002 

1.219202 

i-8i437 

I5-MI76 

5 

127.0003 

1.524003 

2  .  26796 

18.92720 

6 

152.4003 

1.828804 

2.72156 

22.71264 

7 

177.8004 

2    133604 

3-I75I5 

26.49808 

8 

203  .  2004 

2.438405 

3.62874 

30.28352 

9 

228.6005 

2.743205 

4.08233 

34.0^896 

602 


PRACTICAL  MARINE  ENGINEERING. 
METRIC  MEASURES  INTO  ENGLISH. 


Metric. 

Meters  to 
Inches. 

Meters  to 
Feet. 

Kilos  to 
Pounds. 

Liters  to 
Gallons. 

i 

39.3700 

.       3-28083 

2  .  20462 

.26417 

2 

78.7400 

6.56167 

4.40924 

•52834 

3 

118.  i  loo 

9.84250 

6.61386 

.7925i 

4 

157.4800 

13-12333 

8.81849 

1.05668 

5 

I96.85«x) 

16.40417 

11.02311 

1.32085 

6 

236.2200 

19.68500 

13.22773 

1.58502 

7 

275  -59°° 

22.96583 

15.43235 

1.84919 

8 

314.9600 

26.24667 

17.63697 

2.11336 

9 

354.3300 

29.52750 

19.84159 

2-37753 

USE  OF  THE  CONVERSION  TABLES. 

Example  :  Change  243.6  feet  into  meters. 

243.6  =  200  4-  40  -f-  3  +  .6. 

These  parts  separately  may  all  be  directly  converted  from 
the  table  by  an  appropriate  use  of  the  decimal  point.  Thus, 
keeping  simply  three  places  of  decimals : 

200      feet  =  60.960  meters. 

40      feet  =  12.192  meters. 

3      feet  =       .914  meters. 

.6  feet  =       .183  meters. 


Hence,  adding:       243.6  feet  =  74.249  meters. 

Other  examples  may  be  solved  in  an  entirely  similar 
manner. 

[10]    Reduction  of  Compound  Numbers. 

Example — (i)  Reduce  7  miles,  12  rods,  10  feet  to  feet.  We 
may  proceed  in  two  ways :  (a)  We  may  reduce  the  rods  to  feet 
and  add  in  the  10  thus:  12  X  i6J  +  10  =  198  +  10  =  208. 
Then  reduce  the  miles  to  feet  and  add  in  the  208  thus:  7  X 
5,280  +  208  =  36,960  +  208  =  37,i68  feet;  or  (b)  we  may 
reduce  the  miles  to  rods  and  add  in  the  12  thus :  7  X  320  + 
12  =  2,240  +  12  =  2,252.  Then  reduce  the  rods  to  feet  and 
add  in. the  10  thus:  2,252  X  i6J  +  10  =  37,158  +  10  =  37,168 
feet.  The  result  will,  of  course,  be  the  same  in  either  cas^. 
The  factors  for  making  the  reductions  may  be  either  taken 
from  the  tables  of  Sec.  4  or  readily  found  by  separate  com- 
putation. 

Example — (2)  Reduce  37,168  feet  to  miles,  rods  and  feet. 

This  is  the  inverse  of  the  above  and  may  likewise  be  solved 
in  two  ways :  (a)  We  may  reduce  the  feet  to  miles  with  feet" 


COMPUTATIONS  FOR  ENGINEERS.  603 

as  a  remainder,  thus:  37,168  ~  5,280  =  7  miles  and  208  feet 
remainder.  Then  reduce  the  feet  to  rods  with  feet  again  as  a 
remainder,  thus :  208  -f-  i6J  =  12  rods  and  10  feet  remainder. 
Hence,  37,168  feet  —  7  miles,  12  rods,  10  feet;  or  (b)  we  may 
reduce  the  feet  to  rods  with  feet  as  a  remainder,  thus:  37,168 
-f-  i6J  =:  2,252  rods  and  10  feet  remainder.  Then  reduce  the 
rods  to  miles  with  rods  as  a  remainder,  thus :  2,252  -r-  320  = 
7  miles  and  12  rods  remainder.  We  have,  therefore,  as  before, 
37,168  feet  =  7  miles,  12  rods,  10  feet. 

These    examples    will    sufficiently    illustrate    the    mode    of 
procedure  so  that  all  similar  problems  may  be  readily  solved. 


ADDITION,  SUBTRACTION,   MULTIPLICATION  AND  DIVISION  OF 
COMPOUND  NUMBERS. 

[n]  Addition  of  Compound  Numbers. 

Example— Add  the  following: 

16  miles  43  rods 

21  miles          308  rods 

7  miles          318  rods 

44  miles          669  rods  28^  feet 

or  46  miles  30  rods  12    feet 

The  columns  are  added  as  in  whole  numbers  and  the  sums 
are  brought  down.  This  gives  a  correct  result,  but  it  is  not  in 
its  simplest  form,  since  28J  feet  are  more  than  I  rod,  and  669  rods 
are  more  than  i  mile.  We  therefore  reduce  the  feet  to  rods, 
giving  i  rod  and  12  feet,  and  then  carry  the  I  to  the  column  of 
rods,  giving  670.  We  then  reduce  the  rods  to  miles,  giving  2 
miles  and  30  rods,  and  carry  the  2  to  the  column  of  miles,  thus 
giving  the  final  result  as  stated  in  the  second  line  of  the  answer. 

[12]  Subtraction  of  Compound  Numbers. 

Example — In  the  following  subtract  the  lower  from  the 
upper : 

3§  miles  18  rods  14  feet 

21  miles  43  rods  6  feet 


In  the  column  of  rods,  the  43  being  greater  than  the  18, 
we  cannot  subtract  directly,  and  therefore  borrow  i  mile  or  320 
rods  from  the  36  miles,  thus  putting  the  minuend  into  the  form 
as  follows : 

35  m'les          338  rods  14  feet 

2i  miles  43  rods  6  feet 

14  miles          295  rods  8  feet 


604  PRACTICAL  MARINE  ENGINEERING. 

We  may  then  subtract  each  column  as  in  whole  numbers, 
thus  giving  the  result  as  shown.  In  the  actual  operation  the 
borrowing  may  be  done  mentally,  thus  making  it  unnecessary 
to  rewrite  the  minuend  as  shown. 

[13]  Multiplication  of  Compound  Numbers. 

Example — Multiply  14  miles,  276  rods,  12  feet  by  5. 
Operation : 

14  miles  276  rods          12    feet 

5    feet 

70  miles         1,380  rods          60    feet 
74  miles  103  rods          io£  feet 

We  first  multiply  each  term  by  the  multiplier  5  and  obtain  the 
result  entered  in  the  first  line  below.  This  is  correct,  but  not 
in  its  simplest  form,  since  60  feet  are  more  than  i  rod  and  1,380 
rods  more  than  i  mile.  We  therefore  reduce  the  feet  to  rods, 
giving  3  rods  and  10^  feet,  and  carry  the  3  to  the  column  of 
rods,  giving  1,383.  We  then  reduce  the  rods  to  miles,  giving  4 
miles  and  103  rods  and  carry  the  4  to  the  column  of  miles, 
giving  the  final  result  as  stated  in  the  second  line  of  the 
answer. 

[14]  Division  of  Compound  Numbers. 

Example — Divide  142  miles,  296  rods,  15  feet  by  6. 
Operation : 

6)142     miles         296    rods  15    feet 

23!  miles  494  rods  2^  feet 

We  first  divide  each  term  separately  by  the  divisor  6  and  obtain 
the  result  as  written  below  the  line.  This  is  correct,  but  not 
in  its  simplest  form,  since  f  mile  may  be  reduced  to  rods  and 
feet,  and  ^  rod  may  be  reduced  to  feet.  We  therefore  simplify 
as  follows :  23  49  2j 

213  ii 

23  262  13^ 

Since  there  are  320  rods  in  i  mile,  we  have  f  miles  =  f  x 
320  rods  =  213  ^  rods.  We  set  down  the  213  in  the  column 
of  rods,  and,  adding  the  -g-  to  the  other  -^  belonging  with  the 
49,  we  have  f  rod  in  addition.  Since  there  are  i6J  feet  in  I 
rod,  we  have  f  rod  =  f  X  i6J  =  n  feet.  This  we  enter  in 
the  column  of  feet  and  add,  giving  the  final  result  as  shown. 

These  examples  will  sufficiently  illustrate  the  principles  in- 
volved in  the  addition,  subtraction,  multiplication  and  division 


COMPUTATIONS  FOR  ENGINEERS.  605 

of  compound   numbers   so   that   all   similar  problems   may   be 
readily  solved. 

Sec.  5.    DUODECIMALS. 

It  is  often  necessary  to  determine  areas  or  volumes,  the 
dimensions  of  which  are  given  in  feet  and  inches.  To 
this  end  we  may  either  reduce  the  dimensions  to  feet 
and  decimals,  or  treat  them  directly  by  the  method  of 
duodecimals.  In  this  system  of  expressing  numbers,  use  is 
made  of  a  series  of  numerical  units,  each  one-twelfth  of  the 
unit  of  next  higher  order.  The  fundamental  unit  will  be  either 
the  linear  foot,  the  square  foot,  or  the  cubic  foot,  according  to 
the  geometrical  nature  of  the  quantity  to  be  expressed.  Lengths 
are  thus  expressed  in  feet,  inches  and  twelfths;  or,  as  they 
are  termed  feet,  primes  and  seconds.  Similarly  areas  are  ex- 
pressed in  square  feet,  primes  and  seconds,  and  volumes  in 
cubic  feet,  primes  and  seconds,  the  prime  in  each  case 
being  one-twelfth  the  foot,  and  the  second  one-twelfth  the 
prime. 

Duo-decimals  should  be  written  with  a  series  of  accents 
thus:  6°  —  7'  —  10".  The  °  stands  for  the  fundamental  unit, 
the  foot ;  which  may  be  a  length,  an  area  or  a  volume,  accord- 
ing to  the  problem;  the  single  accent  '  stands  for  the  prime, 
and  the  double  accent  "  for  the  second.*  Thus,  if  the  unit 
were  a  foot  of  length,  the  above  expression  would  mean  6  feet, 
7  primes  or  inches,  and  10  seconds  or  -f-|  inch.  If  the  unit 
were  a  square  foot  it  would  mean  6  square  feet,  TV  of  a  square 
foot  and  ||  of  y1^,  or  y1^  of  a  square  foot.  Hence,  in  all,  6 
square  feet  and  94  square  inches.  If  the  unit  were  a  cubic  foot 
it  would  mean  6  cubic  feet,  T7?  of  a  cubic  foot  and  Tf  of  y1^ 
or  y1^  of  a  cubic  foot.  Hence,  in  all,  6  cubic  feet  and  1,128 
cubic  inches.  The  importance  of  noting  the  character  of  the 
fundamental  unit  is  thus  clearly  indicated. 

ADDITION  OF  DUODECIMALS.  The  addition  of  duodecimals 
is  carried  on  exactly  as  in  compound  numbers,  quantities  of  the 
same  order  being  written  under  each  other  and  their  sums, 
where  necessary,  reduced  to  units  of  higher  order  by  division 
by  12. 


*  Care  must  be  taken  to  avoid  confusion  between  this  method  of 
writing  duo-decimals  and  the  common  method  of  expressing  feet  and  inches 
by  one  and  two  accents. 


606  PRACTICAL  MARINE  ENGINEERING. 

Example — Add  I7<>  _  8«  _  I0" 

14°  —  2'  -      9" 

7°  —  i'  —    8" 


Sum:  39°  —  i'  —    3" 

SUBTRACTION  OF  DUODECIMALS.  The  subtraction  of  duo- 
decimals is  carried  on  exactly  as  in  compound  numbers,  quan- 
tities of  the  same  order  being  written  under  each  other  and  units 
of  a  higher  order  being  borrowed  where  necessary.  , 

MULTIPLICATION  OF  DUODECIMALS.  This  operation,  which 
is  the  one  of  greatest  importance  in  the  treatment  of  duo- 
decimals, is  carried  on  according  to  the  following: 

Rule — Set  down  the  two  quantities,  with  terms  of  the  same 
order  under  each  other.  Multiply  each  term  of  the  multiplicand 
by  each  term  of  the  multiplier.  The  order  of  any  such  product 
will  be  determined  by  adding  the  indices  of  the  two  terms  used. 
If  the  product  is  greater  than  12,  reduce  to  the  next  higher 
order  by  dividing  by  12,  and  set  down  the  quotient  and  re- 
mainder in  their  proper  columns.  Proceed  in  this  way,  taking 
care  in  the  product  to  set  down  terms  of  the  same  order  under 
each  other.  Then  add  and  reduce  where  necessary  to  the 
higher  order  by  dividing  by  12. 

Example — Multiply  together : 

6°  _  10'  —  4" 
4°  -    8' 


462 

3  i         8 

24  4         4 


31°         n'        2"        8'" 

We  have  first  8'  X  4"  =  32'"  =  2"  —  8'",  which  is  set  down. 
We  have  next  8'  X  10'  =  80'  =  6'  —  8",  which  is  set  down.  We 
have  next  8'  X  6°  =  48'  =  4°,  which  is  set  down.  In  the  same 
way  we  use  the  other  term  of  the  multiplier,  4°,  and  then  add  and 
reduce  the  columns  as  shown. 

For  purposes  with  which  the  marine  engineer  is  concerned, 
feet  and  inches  are  alone  involved,  and  operations  with  duo- 
decimals are  correspondingly  simplified. 

Examples — (i)  Find  the  area  of  a  boiler  plate  12°  •  —  5'  long 
by  6°  —  f  wide. 

Multiplying  as  before,  we  find  for  the  product  81° — 8'  — 
n",  or  taking  the  result  to  the  nearest  prime,  81°   -9'  or 
square  feet  or  81  square  feet  —  108  square  inches. 


COMPUTATIONS  FOR  ENGINEERS.  607 

(2)  Find  the  volume  of  a  bunker  26°  —  4'  by  9°  —  7'  by 
7°  —  10'. 

Taking  first  the  product  of  26°  -  —  4'  by  9°  —  7'  we  have  252° 

-  4'  —  4".    Then  multiplying  this  by  7°  -  -  10'  we  have  1,976°  — 

10'  —  1 i"  •  —  4"',  or  taking  the  result  to  the  nearest  prime,  1,976° 

-n',  or  1,976  H  cubic  feet  or  1,976  cubic  feet— 1,584  cubic 

inches. 

Sec.  6.     RATIO  AND  PROPORTION. 
[i]  Simple  Proportion. 

The  ratio  between  two  numbers  is  simply  their  numerical 
relationship  expressed  as  the  quotient  of  the  first  divided  by 
the  second.  Thus  the  ratio  of  6  to  3  is  2;  of  1.2  to  3  is  .4;  of 
4  to  5  is  .8,  etc.  Ratio  is  often  expressed  by  the  sign  :  which 
is  simply  an  abbreviation  of  the  sign  of  division  -H.  Thus  6  :  3 
=  2;  1.2  :  3  =  .4,  etc.  Ratio  is  also  expressed  by  the  sign 
of  division  or  in  the  form  of  a  fraction.  Thus 

6:3  or  6      H-  3  or     f     —     2 
1.2  :  3  or  1.2  -T-  3  or  ^-^    =  .4,  etc. 

[i]  A  proportion  is  a  statement  of  the  equality  of  two 
ratios.  The  equality  is  commonly  expressed  by  the  symbol  :  : 

Thus:  6   :  3    :    :  4   :  2 (i) 

A  proportion  may  also  be  written  in  other  ways,  as  follows : 
6:3    =    4-  2 (2) 

I  =  *  (3) 

A  proportion  always  contains  four  terms,  two  for  each 
ratio,  and  when  written  as  in  (i)  and  (2)  the  first  and  last  terms 
are  called  extremes  and  the  second  and  third  are  called  means. 
To  solve  a  proportion  three  terms  must  always  be  known  and 
then  the  remaining  term  can  always  be  found.  From  the  na- 
ture of  a  proportion  it  follows  that  the  product  of  the.  extremes 
must  equal  the  product  of  the  means,  and  this  gives  the  usual 
rule  for  solution  as  follows : 

Rule — If  the  unknown  term  is  an  extreme,  multiply  to- 
gether the  two  means  and  divide  by  the  other  extreme.  If  the 
unknown  term  is  a  mean,  multiply  together  the  two  extremes 
and  divide  by  the  other  mean.  In  either  case  the  quotient  will 
give  the  remaining  term  desired. 

In  a  proportion  two  of  the  terms  always  relate  to  one  kind 
of  quantity,  while  the  other  two  relate  to  another.  Likewise 
two  of  the  terms  always  relate  to  one  set  of  conditions,  while 


6o8  PRACTICAL  MARINE  ENGINEERING. 

the  other  two  relate  to  another  set.  In  problems  to  be  solved 
by  proportion,  therefore,  where  three  terms  must  be  given, 
two  terms  will  be  of  one  kind  and  the  remaining  term  will  be  of 
another  and  of  the  same  kind  as  the  answer.  Also  two  terms 
will  relate  to  the  given  set  of  conditions,  and  the  remaining 
term  to  the  set  involving  the  unknown  term  or  answer. 

Again,  proportions  are  of  two  kinds,  direct  and  inverse. 
In  a  direct  proportion  the  relation  between  the  two  quantities 
different  in  kind  is  such  that  both  increase  or  decrease  to- 
gether. In  an  inverse  proportion  the  relation  between  these 
two  quantities  is  such  that  one  increases  as  the  other  decreases. 
Thus  if  the  question  involves  the  relation  between  distance  and 
speed,  the  time  being  the  same,  the  proportion  is  direct,  be- 
cause, for  a  given  time,  the  more  speed  the  more  distance,  or 
the  more  distance  the  more  speed.  On  the  other  hand,  if  the 
question  involves  the  relation  between  speed  and  time  for  a 
given  distance,  the  proportion  is  inverse,  because  for  a  given 
distance  the  more  speed  the  less  time,  or  the  more  time 
the  less  speed,  and  vice  versa.  Our  general  knowledge  of  the 
relation  between  the  quantities  involved  will  thus  enable -us  to 
determine  whether  the  proportion  will  be  direct  or  inverse. 

Example  of  a  direct  proportion  : 

If  a  ship  steams  1,400  miles  in  5  days,  how  far  will  she 
steam  in  8  days  at  the  same  rate? 

Here  two  of  the  given  terms  are  days  and  one  is  miles,  be- 
ing of  the  same  character  as  the  answer  desired.  Also  two 
relate  to  one  performance  or  set  of  conditions  (1,400  in  5  days), 
while  the  other  relates  to  another  set  (the  desired  performance 
in  8  days).  Our  right  to  solve  this  example  by  direct  propor- 
tion lies  in  the  fact  that  the  relation  between  the  5  days  and 
1,400  miles  must  be  the  same  as  that  between  the  8  days  and 
the  distance  desired,  and  hence  there  must  be  an  equality  in  the 
ratios  showing  these  relations,  and  similarly  for  problems  of 
like  character. 

A  simple  direct  ( proportion,  like  that  involved  in  the  ex- 
ample above,  may  be  stated  in  various  ways,  of  which  two  will 
serve  our  present  purpose. 

(2)  (2)  (I)  (I) 

(a)  Ans.   (miles)  :         8  (days)    :  :   1400  (miles)  :  5  (days) 

(2)  (i)  (2)  (i) 

(b)  Ans.   (miles)  :  1400  (miles)  :  :         8  (days)  :  5  (days) 


COMPUTATIONS  FOR  ENGINEERS.  609 

The  numbers  in  (  )  relate  to  the  two  sets  of  conditions,  the 
first  being  the  set  given,  and  the  second  being  the  set  for  which 
the  distance  is  desired.  It  is  thus  seen  that  the  proportion  may 
be  stated  as  in  (a),  with  each  set  of  conditions  forming  a  ratio, 
the  items  of  proportion  alternating :  miles,  days,  miles  days ;  or 
it  may  be  stated  as  in  (b),  with  the  set  of  conditions  alternating 
2d,  ist,  2d,  ist,  the  two  items  of  each  ratio  being  the  same. 

Example  of  an  inverse  proportion  : 

If  a  ship  at  10  knots  does  a  certain  trip  in  5  days,  how  many 
days  will  be  required  at  12  knots? 

The  relation  between  time  and  speed,  as  we  know,  is  such 
that,  for  a  given  distance,  the  more  speed  the  less  time,  or  the 
less  speed  the  more  time.  The  time  is,  therefore,  said  to  be  in 
such  case  inversely  proportional  to  the  speed.  That  is,  for  ex- 
ample, if  the  speed  is  doubled  the  time  will  be  halve'd,  etc. 

An  inverse  proportion  may  be  stated  as  follows : 

(2)  (I)  (I)  (2) 

(c)  Ans.   (days)  :   10  (knots)    :    :     5  (days)    :   12  (knots) 

(2)  (I)  (I)  (2) 

(d)  Ans.   (days)  :     5  (days)     :    :   10  (knots)  :   12  (knots) 

The  difference  between  these  methods  of  statement  and 
those  above  for  direct  proportion  will  be  readily  seen  by  com- 
parison. 

As  another  general  way  of  stating  a  proportion  whether 
direct  or  inverse  we  may  proceed  as  folows : 

Put  the  anszver,  or  letter  representing  it,  for  the  first  term, 
and  the  other  quantity  of  the  same  kind  for  the  second  term. 
Then,  according  as  the  first  term  or  answer  should  be  greater 
or  less  than  the  second  term,  write  the  third  and  fourth  terms 
in  the  same  order.  That  is  if  the  relation  of  the  quantities  is 
such  that  the  answer  should  be  greater  than  the  second  term, 
write  the  third  and  fourth  terms  in  the  order  greater  —  lesser: 
or  if  the  answer  should  be  less  than  the  second  term,  write  the 
third  and  fourth  terms  in  the  order  lesser  —  greater. 

After  having  become  familiar  with  the  methods  of  stating 
a  proportion,  the  names  of  the  quantities  and  the  numbers  de- 
noting the  sets  of  conditions  may,  of  course,  be  omitted,  and  we 
should  have  instead  of  (a)  and  (b) 

Ans.   :        8   :   :  1400   :  5 
Ans.    :  1400   :    :         8:5 


6io  PRACTICAL  MARINE  ENGINEERING. 

Solving  either  of  these  according  to  the  rule  given,  we 
have: 

Distance  =  8  X  1400  -=-  5  =  2240  ans. 
Likewise  instead  of  (c)  and  (d)  we  should  have : 
Ans.    :  10    :    :     5    :  12 
Ans.    :     5    :   :  10   :  12 
Solving  either  of  these  we  have : 

Days  —  5   x    10  -5-  12   =  50  -i.  12   =  4^  Ans. 

[2]  Compound  Proportion. 

In  many  cases  the  result  depends  on  more  than  one  chang- 
ing condition.  In  such  case  the  problem  is  treated  by  the 
method  of  compound  proportion  as  iljustrated  in  the  following 
example. 

When  coal  is  $4.20  per  ton  the  fuel  bill  for  a  ship  requiring 
34  tons  per  day  on  a  voyage  of  2,100  miles  is  $1,020.  At  the 
same  speed  what  would  be  the  bill  on  a  2,8oo-mile  voyage,  with 
coal  at  $3.60  per  ton,  and  a  consumption  of  40  tons  a  day? 

The  resulting  cost  evidently  depends  on  three  conditions, 
and  the  proportion  is  stated  as  follows : 

3.60   :         4.20 

Ans.    :  1020   :    :       40        :       34. 
2800        :  2100 

This  consists  really  of  three  simple  direct  proportions, 
each  stated  exactly  according  to  the  rules  already  given,  as 
may  be  readily  seen.  For  the  solution  of  such  a  proportion 
the  same  rules  may  be  used,  but  the  "product  of  the  means" 
or  the  "product  of  the  extremes"  must  here  be  understood  to 
mean  the  product  of  all  the  separate  numbers  forming  these 
terms. 

Thus  for  the  foreging  proportion  we  multiply  together 
the  means  and  divide  by  the  extremes,  giving  as  follows  : 

Ans.  =3.6o  x   4°  X   2800  x   102°  =  $I37I.43. 
4.20   X   34   X    2100 

Cancellation  can  usually  be  made  to  assist  in  the  reduc- 
tion of  such  expressions,  and  we  thus  readily  find  the  answer  as 
stated. 

Where  the  relations  are  such  that  the  answer  is  inversely 
proportional  to  certain  of  the  varying  conditions,  the  ratio  in- 
volving these  conditions  must,  of  course,  be  so  stated  as  to 
make  this  part  of  the  proportion  inverse  instead  of  direct.  In 


COMPUTATIONS  FOR  ENGINEERS.  611 

fact,  each  of  the  ratios  in  the  second  part  of  the  proportion 
should  be  carefully  examined  in  order  to  make  sure  whether 
it  should  be  stated  direct  or  inverse. 

Example  involving  both  direct  and  inverse  proportion: 
When  coal  is  $4.00  per  ton,  the  fuel  bill  for  steaming  a 
certain  distance  at  a  speed  of  12  knots,  with  a  ship  requiring 
48  tons  per  day,  is  $1,800.  For  the  same  distance,  what  would 
be  the  bill  if  the  ship  steams  10  knots  on  40  tons  per  day,  with 
coal  at  $3.20  per  ton? 

The  statement  would  be  as  follows: 

3.20   :  4.00  (direct) 
Ans.    :  1800    :    :  12         :      10  (inverse) 

40        :      48  (direct) 
In  this  case  we  have  : 


Ans.  =  x   3-2^_X    I2   X   4Q 

4.00  x   i°  X  48 

PROBLEMS  IN  PROPORTION. 

(1)  An  engine  with  34  Ib.  mean  effective  pressure  gives 
1,400  I.H.P.     All  other  conditions  remaining  the  same,  what 
would  the  engine  give  with  39  Ib.  mean  effective  pressure? 

Ans.  i  ,606  I.H.P. 

(2)  An  engine  making  98  revolutions  per  mt.  gives  1,800 
I.H.P.     All  other  conditions  remaining  the  same,  what  would 
the  engine  give  if  the  revolutions  were  90? 

Ans.  1,653  I.H.P. 

(3)  An  engine  with  stroke  of  3  ft.  gives  900  I.H.P.     All 
other    conditions    remaining    the    same,    what    would    be    the 
power  with  stroke  of  42  in.? 

Ans.  1,050  I.H.P. 

(4)  An  engine  cylinder  whose  area  is   1,200  sq.  in.  gives 
800   I.H.P.     All   other   conditions   remaining  the   same,   what 
would  be  the  power  with  an  area  of  1,000  sq.  in.? 

Ans.  666.67  I.H.P. 

(5)  A  given  engine  has  mean  effective  pressure  33,  revolu- 
tions 120,  stroke  42  in.,  and  gives  1,800  I.H.P.     Other  condi- 
tions remaining  the   same,  what  would  be  the  power  with  a 
mean  effective  pressure  of  38,  revolutions  of  100  and  stroke 
of  4  ft.? 

Ans.  1,974  I.H.P. 


612  PRACTICAL  MARINE  ENGINEERING. 

(6)  A  boiler  with  tubes  7  ft.  long,  and  2^4  in.  diam.,  has 
2,168  sq.  ft.  of  tube-heating  surface.     What  would  be  the  sur- 
face, with  the  same  number  of  tubes,  7  ft.  6  in.  long  and  2^2 
in.  diam.? 

Ans.   2,112  sq.  ft. 

(7)  An  engine  with  34  Ibs.  mean  effective  pressure  and  98 
revolutions  develops  a  certain  power.     If  the  mean   effective 
pressure  were  38  Ibs.,  what  revolutions  would  give  the  same 
power? 

Ans.   87.7  rev. 

(8)  A  given  engine  has  a  mean  effective  pressure  33,  revo- 
lutions 120,  stroke  42  in.,  and  develops  a  certain  power.     With 
mean  effective  pressure  of  38  and  stroke  of  3  ft.,  what  would 
be  the  revolutions  for  the  same  power? 

Ans.  121.6  rev. 

(9)  A  pump  making  40  double  strokes  per  mt.  can  empty 
a  tank  in  i|  hrs.     In  what  time  could  the  same  pump,  making 
30  double  strokes  per  mt.,  empty  a  second  tank,  20  per  cent 
larger  than  the  first? 

Ans.  2.4  hours. 

(10)  A  propeller  at  100  revolutions  and  20  per  cent  slip 
gives  a  speed  of  18  knots.    What  will  be  the  speed  at  120  revo- 
lutions and  25  per  cent  slip? 

Ans.  20.25  knots. 

Sec.  7.  EVOLUTION  AND  INVOLUTION.* 

[i]  EVOLUTION  is  the  operation  of  raising  a  number  to 
successive  powers,  or  of  multiplying  it  into  itself  as  a  factor  a 
certain  number  of  times.  The  number  of  times  the  number  is 
used  as  a  factor  is  called  the  index  of  the  power,  and  is  indicated 
by  a  small  figure  written  to  the  right  and  above  as  follows : 

42   =  4  X   4  =   16 
53  =  5   X   5   X   5   =   ^5 
35   =  3X3X3X3X3   =   243 

Evolution  involves,  therefore,  simply  continued  multiplica- 
tion. The  powers  most  commonly  used  by  the  engineer  are 

*  Hand  books  with  convenient  tables  of  powers  and  roots  are  so  com- 
mon at  the  present  day  that  the  engineer  has  small  use  for  the  actual 
operations  of  raising  to  powers  or  of  extracting  roots.  In  practice  the  use 
of  such  tables  is  always  counseled  as  tending  toward  accuracy  and  speed. 
The  importance  of  these  operations,  however,  merits  a  brief  outline  of 
the  process  as  given  herewith. 


COMPUTATIONS  FOR  ENGINEERS.  6i3 

the  second  and  third,  or  square  and  cube,  as  they  are  commonly 
called. 

INVOLUTION  is  the  inverse  of  evolution,  and  consists 
in  finding  a  number  which,  used  on  itself  as  a  factor  a  certain 
number  of  times,  will  produce  a  given  number.  The  former  is 
then  called  the  root  of  the  latter.  The  number  of  times  the 
root  is  used  as  a  factor  is  called  the  index,  and  is  represented 
either  by  writing  this  number  at  the  upper  left  hand  angle  of 
the  sign  of  involution,  \/  ,  or  by  the  use  of  a  fractional  index, 
written  as  in  evolution.  The  roots  most  commonly  used  by 
the  engineer  are  the  square  and  cube  roots,  corresponding  to 
the  second  and  third  or  square  and  cube  powers.  When  square 
root  is  indicated  by  the  symbol  y  ,  it  is  customary  to  omit 
the  2  from  the  upper  angle.  Thus  we  have : 

3 

1/27  or  (27)4  =  3  because  3  x  3  X  3  =  27- 
1/49  or  (49)2  =  7  because  7  x  7  =  49- 

Occasionally  the  engineer  has  to  deal  with  the  index  -f. 
which  is  simply  a  short  way  of  indicating  two  operations,  (i) 
Raising  to  the  square.  (2)  Extracting  the  cube  root.  Thus 
64!  means  the  3d  root  of  the  2d  power  of  64,  or  the  2d  power 
of  the  3d  root  of  64.  Either  order  of  operation  will  give  the 
same  result.  Thus: 


(64) 6  =  1/64  x  64  =  1/4096  =  16 

'2  3   2 

or  (64) 3  =  (1/64)  =  42  =  16 

[2]    To  Extract  the  Square  Root. 

This  is  best  illustrated  by  an  example.  Find  the  square 
root  of  746.2. 

Rule* — (i)  Point  off  the  given  number  into  periods  of  two 
figures  each,  beginning  at  the  right  or  at  the  decimal  point,  if 
there  is  one,  and  in  the  latter  case  point  both  ways,  adding 
ciphers  on  the  right  of  the  decimal  as  may  be  necessary  to 
complete  the  periods.  Thus: 


*  The  brackets  [  ]  contain  the  numbers  in  the  example  which  corre- 
spond to  the  special  indication  of  the  rule,  and  thus  make  its  application  to 
the  given  case  more  easily  followed. 


*i4  PRACTICAL  MARINE  ENGINEERING. 

Number  Pointed  off. 

2643          26-43 

867  8-67 

424-362 4-24.36-20 

. 024 .02-40 

.6     60 

(2)  Write  a  o  on  the  left,  thus  heading  two  columns  (i) 
and  (2),  as  shown.  Find  by  trial  the  greatest  number  [2]  which 
when  squared  is  equal  to  or  less  than  the  left  hand  period.  Put 
this  on  the  right  as  the  first  figure  of  the  root. 

(I)  (2) 

o  7-46.20(27.316  4- 

2  4 


2  346 

2  329 

40  1720 

7  1629 

47  9120 

7  546i 


540  363900 

3 

543 
3 

5460 

i 


54620 

(3)  Place  this  figure  [2]   under  the  o  in  col.  (i)  and  add. 
Multiply  the  sum   [2]   by  the  root  figure   [2],  and  place  the 
product  [4]  Under  the  left  hand  period  in  col.  (2).    This  product 
will  be,  of  course,  the  square  of  the  root  figure.     Subtract  and 
bring  down  the  next  period  for  a  partial  dividend  [346]  . 

(4)  Again  place  the  root  figure  [2]  on  the  left  and  add  [4]  . 
Annex  a  o  and  the  result  [40]  will  be  a  trial  divisor  for  the  next 
root  figure. 

(5)  Divide  and  take  on  trial  the  resulting  whole  number 
for  the  next  root  figure  [7]. 

(6)  Bring  down  this  figure  [7]  in  col.  (i)  under  the  o.    Add 
and  multiply  the  sum   [47]    by  the  same  root  figure    [7]    and 
place  the  product  [329]   in  col.  (2)  under  the  partial  dividend. 
Subtract  and  bring  down  as  before  for  a  new  partial  dividend 
[1720]. 


COMPUTATIONS  FOR  ENGINEERS.  615 

(7)  Place  the  root  figure    [7]    again  in  col.  (i),  add  and 
annex  a  cipher  for  a  new  trial  divisor  [540]. 

(8)  Find  another  root  figure  as  before  and  proceed  in  this 
manner  till  as  many  figures  are  obtained  as  are  desired. 

If  the  product  found,  as  in  (6),  is  greater  than  the  partial 
dividend,  it  indicates  that  the  trial  figure  was  too  great,  and 
the  next  lower  must  be  taken.  If  at  any  time  the  trial  divisor  is 
greater  than  the  partial  dividend,  enter  a  o  in  the  root,  bring 
down  the  next  period  in  col.  (2)  for  a  new  partial  dividend,  an- 
nex a  o  on  the  right  in  col.  (i)  for  a  new  trial  divisor  and  pro- 
ceed as  before. 

[3]    To  Extract  the  Cube  Root. 

This  is  best  illustrated  by  an  example.  Find  the  cube 
root  of  12.593. 

(i)  (2)  (3) 

o  o  12.593  (23.26 

2  4  8 

2  "  4  4593 

2  8  4167 


4   66      1200  426000 

2    3       189  320168 

60  690      1389  105832000 

J  _!      I9§ 
63  692      158700 
3    2       1384 

694     160084 

2  1388 

6960  I6I47200 

Rule — Point  off  the  given  number  into  periods  of  three 
figures  each,  beginning  at  the  right  or  at  the  decimal  point, 
if  there  is  one,  and  in  the  latter  case  point  both  ways,  adding 
ciphers  on  the  right  of  the  decimal  as  may  be  necessary  to  com- 
plete the  periods.  Thus : 

Number  Pointed  Off. 

1724  I'724 

17243  17*243 

I7-24      17.240 

.64      .  640 

.  0032 .  003  '  2OO 

(2)  Write  ciphers  on  the  left  thus,  heading  the  columns 
(i),  (2)  and  (3),  as  shown.  Find  by  trial  the  greatest  number 
[2]  which  when  cubed  is  equal  to  or  less  than  the  left  hand 
period.  Put  this  on  the  right  as  the  first  figure  of  the  root. 


616  PRACTICAL  MARINE  ENGINEERING. 

(3)  Place  this  figure  under  the  o  in  col.  (i),  add,  multiply 
sum  [2]  by  root  figure  [2],  place  product  [4]  in  col.  (2),  add, 
multiply  sum  [4]   by  root  figure   [2]   again,  and  place  product 
[8]  in  col.  (3)  under  left  hand  period.    This  product  will  be,  of 
course,  the  cube  of  the  root  figure.     Subtract  and  bring  down 
the  next  period  for  a  partial  dividend  [4593]. 

(4)  Again  place  the  root  figure  [2]  in  col.  (i),  add,  multiply 
sum   [4]   by  root  figure,  put  the  product   [8]   in  col.  (2),  and 
add  [12]. 

(5)  Again  place  the  root  figure  [2]  in  col.  (i),  and  add  as 
before  [6] . 

(6)  Annex  one  o  to  the  result  in  col.  (i)  [60]  and  two  os 
to  that  in  col  (2)  [1200] .    The  latter  is  then  a  trial  divisor  for  the 
next  root  figure,  which  is  thus  seen  to  be  probably  3. 

(7)  The  same  process  of  bringing  down,  adding  and  multi- 
plying in  cols,  (i),  (2)  and  (3)  is  then  repeated  as  just  described, 
and  as  shown  in  the  example.     Continue  in  this  wray  until  as 
many  figures  of  the  root  are  found  as  are  desired. 

If  the  final  product  to  be  entered  in  col.  (3)  is  greater  than 
the  partial  dividend,  it  indicates  that  the  trial  figure  was  too 
great,  and  the  next  lower  must  be  taken.  If  at  any  time  the  trial 
divisor  is  greater  than  the  partial  dividend,  enter  a  o  in  the  root, 
bring  down  the  next  period  in  col.  (3)  for  a  new  partial  dividend, 
annex  one  o  in  col.  (i)  and  two  os  in  col.  (2)  for  a  new  trial 
divisor,  and  proceed  as  before. 

It  will  be  noted  lhat  in  these  methods  for  square  and  cube 
root  the  former  requires  for  each  root  figure  two  operations  in 
col.  (i)  and  one  in  col.  (2),  while  the  latter  similarly  requires 
three  operations  in  col.  (i),  two  in  col.  (2),  and  one  in  col.  (3). 
Care  should  be  taken  that  none  of  these  are  omitted,  and  that 
the  entire  process  is  carried  through  with  regularity  and  order. 

Sec.  8.   MATHEMATICAL  SIGNS,  SYMBOLS  AND 
OPERATIONS. 

Mathematical  signs  are  simply  shorthand  methods  of 
indicating  mathematical  language.  Those  most  commonly  met 
with  are  the  following: — 

+  The  sign  of  addition  called  plus.  This  means  that  the 
two  numbers  or  quantities  between  which  it  is  placed  are  to  be 
added.  Thus  12  +  3  is  read  12  plus  3  and  means  that  12  and  3 
are  to  be  added,  the  result  being  15. 


COMPUTATIONS  FOR  ENGINEERS.  617 

—  The  sign  of  subtraction  called  minus.  This  means  that 
the  number  or  quantity  which  follows  the  sign  is  to  be  subtracted 
from  that  which  precedes  it.  Thus  12  —  3  is.  read  12  minus  3 
and  means  that  3  is  to  be  taken  from  12,  the  result 
being  9. 

X  The  sign  of  multiplication.  This  means  that  the  two 
numbers  or  quantities  between  which  it  is  placed  are  to  be  mul- 
tiplied together.  Thus  12  X  3  is  read  12  times  3  or  12  multi- 
plied by  3,  the  result  being  36. 

-r-  The  sign  of  division.  This  means  that  the  number  or 
quantity  which  precedes  the  sign  is  to  be  divided  by  that  which 
follows.  Thus  12  -r-  3  is  read  12  divided  by  3,  the  result 
being  4. 

/  A  sign  of  division.  A  fraction  is  really  a  mode  of  ex- 
pressing division,  and  a  common  way  of  writing  a  fraction  all  in 
one  line  is  to  make  use  of  the  oblique  line.  Thus  12/3  means 
the  same  as  -^  or  12  -f-  3  or  4.  Frequently  the  horizontal  line 
—  as  shown  is  used,  thus:  ^,  ^,  1-2  all  indicate  one-half,  or  I 
divided  by  2.  The  horizontal  line  used  in  this  connection  must 
not  be  confused  with  the  minus  sign ;  usually  the  sense  is  plainly 
indicated  by  the  connection  in  which  it  is  used. 

.  Placed  before  and  in  line  with  the  bottom  of  a  number  is  a 

decimal  point,  showing  that  the  number  is  the  numerator  of  a 

fraction  which  has  some  power  of  10  for  its  denominator;  as  .1 

=  TV  -25  =  T\\,  which  reduced  to  its  lowest  terms  is  1-4.     See 

section  2. 

:  The  sign  of  ratio.  This  signifies  the  ratio  or  numerical  re- 
lationship of  the  two  quantities  between  which  it  is  placed,  and  is 
equivalent  to  a  sign  of  division,  since  the  quotient  of  the  first 
quantity  divided  by  the  second  is  the  measure  of  the  ratio  be- 
tween them.  Thus  12  :  3  is  read  the  ratio  of  12  to  3  or  12  is  to 
3,  and  the  real  measure  of  this  ratio  is  12  -f-  3  or  4. 

The  sign  of  proportion  or  equality  of  ratios.  This  sign 
is  placed  between  two  ratios  and  signifies  that  they  are  equal. 
Thus  12  :  3  ::  20  :  5  is  read  12  is  to  3  as  20  is  to  5,  or  the 
ratio  of  12  to  3  equals  the  ratio  of  20  to  5.  This  is  seen  to  be 
the  case  since  4  is  the  measure  of  each  ratio. 

=  The  sign  of  equality.  This  signifies  that  the  two  quanti- 
ties separated  by  the  sign  are  equal  in  value.  Thus  12-^3  =  4 
is  read  12  divided  by  3  equals  4,  and  thus  states  the  equality  be- 
tween the  two  sides  of  the  relationship. 


618  PRACTICAL  MARINE  ENGINEERING. 

Equation.  Two  quantities  or  expressions  related  by  the  sign 
of  equality,  =,  form  an  equation.  Thus 

4  +  2  =  6 

a  =  3 

a  +  b  —  c 

(  ),     [],  i.       Parentheses    or    brackets.     These    symbols 

mean  that  all  numbers  or  quantities  within  a  parenthesis  or  pair 
of  brackets  are  to  be  considered  as  one  quantity  and  thus  treated 
in  all  numerical  operations.  Thus  2  (3  +  4)  means  that  3  +  4 
is  to  be  taken  as  the  single  quantity  7,  and  then  multiplied  by  2. 
Similarly  2  (  3+4 — 2)=io 

3   [16-2  (3+4-2)]  =18 

NOTE:  The  sign  multiplication,  X,  is  often  omitted  between 
a  number  and  a  parenthesis  or  bracket  containing  a  quantity 
into  which  it  is  to  be  multiplied,  as  in  the  expressions  here 
shown. 

In  some  cases  a  bar  or  vinculum  is  drawn  over  numbers  thus 
to  be  taken  together.  Thus  2X3  +  6  means  2  multiplied  by 
the  quantity  3  +  6,  or  2  X  9>  or  18.  The  difference  between 
2X3  +  6  and  2X3  +  6  or  12  will  be  noted.  In  reducing 
quantities  thus  affected  by  the  signs  +,  — ,  X,  -r-  and  connected 
by  brackets,  the  difference  in  significance  between  the  sign  +,  — 
and  X  -r-  must  be  carefully  noted.  Thus  2X3  +  6  means  2 
times  3  added  to  6  or  12  and  not  2  times  (3+6)  or  18.  As  a 
general  principle,  it  may  be  remembered  that  the  signs  +  and 
—  effect  a  separation  of  the  expression  into  separate  terms,  while 
the  signs  .X  and  -r-  bind  together  the  two  quantities  between 
which  they  stand  into  a  single  term. 

Examples — These  principles  are  further  illustrated  by  the 
following : 

3X16  —  2X3  +  4--2  +  4X3--1  =55 
3[i6  — 2  x  3  +  4  — 2  +  4  X  3  --  i]  =  69 
3[i6  —  2  (3  +  4)  -  -  2  +  4  (3  -  -  i)]  =26 

3fi6  —  2  (3  +  4  -  -  2)]  +  4  (3  -  -  i)  =  24 

I/'         This  sign  placed  over  a  quantity  denotes  the  extraction 

of  a  root.     If  no  number  is  placed  at  the  upper  left  angle, 

it  denotes  the  square  root;  otherwise  a  root  corresponding 

to  the  index  thus  indicated. 

Thus  |/  49  denotes   the    square   root  of    49  or  7,    ->/  27 


COMPUTATIONS  FOR  ENGINEERS.  619 

4 

denotes  the  cube  root  of  27  or  3,  1/76  denotes  the  fourth 

root  of  1 6  or  2,  etc. 
32  or  43  or  a4.    A  small  number  written  to  the  right  and  above 

another  number  or  quantity  is  called  an  index  or  exponent, 

and  signifies  that  the  lower  number  or  quantity  is  to  be 

used  as  a  factor  on  itself  a  number  of  times  equal  to  the 

index.     Thus : 

32  =  3  X  3  =  9 
43  =  4X4X4  =  64 
a4  =  aXaXaXa 
' "     These  signs  set  to  the  right  and  above  any  figure  or  figures 

(superior)  signify  feet  and  inches.     These  signs  are  much 

used  in  dimensioned  drawings. 
J__     Signifies  perpendicular  to. 
(_      Signifies  .angle. 
L     Signifies  right  angle. 
.  *.     Signifies  hence  or  therefore. 
'.'    Signifies  because. 
TT       Denotes  the  ratio  between  the  circumference  and  diameter 

of  a  circle.    Its  value  is  usually  taken  as  3.1416. 
G     Square  sometimes  used  in  denoting  pressures ;  as  220  Ibs. 

per  D"  or  per  square  inch. 
%     Signifies  per  centum  or  per  hundred. 

FORMULAE. 

A  formula  is  simply  a  brief  way  of  denoting  a  series  of 
mathematical  operations.  Once  understood,  the  directions  given 
by  a  formula  are  much  more  readily  followed  than  when  given 
in  the  form  of  a  rule.  In  fact  a  formula  may  be  considered  as 
simply  a  brief  or  short  hand  way  of  expressing  the  same  direc- 
tions as  are  given  by  the  rule  in  ordinary  words.  In  formulae, 
quantities  are  usually  represented  by  letters,  as  in  the  well- 
known  horse  power  formula : 

LH  P  - 2  P  LA N 
33,000 

In  this  formula  p  denotes  the  mean  effective  pressure  per 
square  inch  of  piston  area,  L  the  length  of  stroke  in  feet,  A  the 
piston  area  in  square  inches,  and  N  the  revolutions  per  minute. 

In  thus  writing  letters  to  represent  quantities  the  sign  of 
multiplication,  X,  is  usually  omitted.  Thus  in  the  foregoing  the 
numerator  2  p  L  A  N  means  the  same  as 


620  PRACTICAL  MARINE  ENGINEERING. 

or  that  the  continued  product  is  to  be  taken  of  these 
five  factors.  It  must  be  noted,  however,  that  where  both  factors 
are  numbers  the  sign  for  multiplication  cannot  be  omitted.  Thus, 
23  does  not  mean  2  X  3,  but  20  +  3  or  23. 

Division  may  be  expressed  by  the  usual  sign,  but  it  is  more 
commonly  indicated  by  writing  the  dividend  as  the  numerator 
and  the  divisor  as  the  denominator  of  a  fraction.  Or  in  general 
we  multiply  by  putting  a  factor  in  the  numerator,  and  divide 
by  putting  a  factor  in  the  denominator.  Thus  in  the  horse  power 
formula  the  product  2  p  L  A  N  is  to  be  divided  by  33,000. 

As  a  further  illustration,  take  the  formula 

P-7^ 
~  6A! 

In  this  formula  p  is  the  pressure  per  square  inch  in  a  boiler,  T 
is  the  tensile  strength  of  the  material  of  the  shell,  t  is  the  thick- 
ness of  the  plate,  and  R  is  the  half  diameter  or  radius  of  the 
shell.  The  whole  gives  the  pressure  per  square  inch  allowed  by 
U.  S.  rules  on  marine  boilers.  The  formula  directs  us,  in  order 
to  find  the  desired  pressure,  to  multiply  together  T  and  t  and  to 
divide  the  product  by  6  times  R',  or,  in  the  words  of  the  U.  S. 
rule  :  "Multiply  one-sixth  of  the  lowest  tensile  strength  .  .  . 
by  the  thickness  .  .  .  and  divide  by  the  radius  or  half 
diameter."  In  this  formula  all  dimensions  are  in  inches  and  the 
result  is  the  pressure  per  square  inch  allowed  on  the  boiler. 
Thus  let  T  =  60,000,  t  —  1/4  in.  and  R  =  6  feet  or  72  in.  Then  : 

60,000   x  1.2=5  -,  .     7 

p  —  -  -=174  pounds  per  square  inch. 

Take  again  the  formula 


In  this  formula  p  is  the  pressure  per  square  inch  allowed  on 
a  flat  surface  of  a  boiler  supported  by  staybolts,  t  is  the  thickness 
of  the  plate  expressed  in  sixteenths,  and  L  is  the  pitch  of  the 
bolts,  or  distance  from  center  to  center.  The  formula  thus 
directs  us  to  multiply  112  by  the  square  of  the  thickness  of  the 
plate  in  sixteenths,  and  then  to  divide  the  product  by  the  square 
of  the  pitch  of  the  bolts.  Thus  let  the  thickness  be  9-16  in.  and 
pitch  be  7  in.  Then  we  have  : 

/  —  II2    X    9  X  9  _  l85  pounds  per  square  inch. 


COMPUTATIONS  FOR  ENGINEERS. 


621 


Sec.  9.     GEOMETRY  AND  MENSURATION.* 

[i]    Square. 

A  square  is  a  figure,  such  as  A  B  C  D,  having  four  sides  all 
equal,  and  four  angles  all  equal,  each  being  a  right  angle. 

DIAGONAL,  A  C.  To  find  the  length  of  a  diagonal,  A  C,  hav- 
ing given  a  side  of  the  square,  as  A  B : 

B     C 


Rule  —  Square  the  side,  multiply  by  2,  and  take  the  square 


root; 


or  A  C  = 


512  = 


or  Rztle  —  Multiply  the  side  by  1.4142. 

Example:   A  B  =  16.     Then  A  C  =  V  2  x  256  = 
22.627, 

or  A  C  —  16  x   1.4142  =  22.627. 

AREA,  A  B  C  D.     To  find  the  area  of  a  square,  having 
given  the  length  of  a  side,  as  A  B  : 

*  The  following  definitions  are  here  given  as  introductory  to  this  sec- 
tion. Other  definitions  will  be  given  as  the  terms  are  introduced. 

An  angle  is  formed  when  two  lines,  O  A  and  O  B,  having  different 
directions  meet  in  a  point,  as  O.  The  angle  refers,  then,  to  the  difference 
in  direction  of  the  two  lines,  and  its  measure  is  a  measure  of  such  difference 
in  direction.  An  angle  is  usually  denoted  by  three  letters,  the  one  at  the 
apex  being  placed  between  the  other  two.  Thus,  in  Fig.  a  the  angle  would 
be  called  A  O  B  or  B  O  A. 

D 


When  a  line,  CD,  meets  another  line,  A  B,  in  such  a  way  that  the  four 
angles  at  E  are  all  equal,  the  two  lines  are  said  to  be  perpendicular  to  each 
other,  or,  in  more  common  terms,  one  line  is  square  with  the  other.  An 
angle  such  as  those  formed  at  E  is  called  a  right  angle. 

An  angle  less  than  a  right  angle,  as  A  O  B,  Fig.  a,  is  called  an  acute 
angle.    An  angle  greater  than  a  right  angle,  as  F E  B,  Fig.  b,  is  called 
obtuse  angle. 


an 


622  PRACTICAL  MARINE  ENGINEERING. 

Rule — Square  the  side,  or  multiply  it  by  itself; 

or  Area  -  AH?  =  A  B  x  A  B. 
Example:   A  B  —  6.     Then  area  =  6  x  6  =  36. 

[2]  Rectangle. 

A  rectangle  is  a  figure,  such  as  A  B  C  D,  having  four  sides, 
the  opposite  sides  being  equal  and  parallel  (A  B  =  D  C  and 
B  C  =  A  D),  and  four  angles  all  equal,  each  being  a  right  angle. 

DIAGONAL,  B  D.  To  find  the  length  of  a  diagonal,  B  D 
having  given  the  two  sides,  as  B  C  and  C  D : 

Rule — Square  the  two  adjacent  sides,  add,  and  take  the 
square  root; 

or  B  D 


Example  :  B  C  =  6,  C  D  =  8.      Then  B  D  =  V  36  +  64 

—  \/   100   —    10. 

AREA,  A  B  C  D.  To  find  the  area  of  a  rectangle,  having 
given  the  two  sides,  as  A  B  and  A  D : 

Rule — Find  the  product  of  the  two  adjacent  sides  ; 

or  Area  =  A  B  X  A  D. 
Example:    A  B  =  6,  A  D  ==  8.    Then  area  =  6  X  8  =  48. 

[3]  Parallelogram. 

A  parallelogram  is  any  figure,  such  as  A  B  C  D,  having  four 
sides  and  four  angles,  the  opposite  sides  being  equal  and 
parallel,  and  the  oposite  angles  being  equal. 


AREA,  A  B  C  D.  To  find  the  area  of  a  parallelogram,  hav- 
ing given  a  side  and  the  perpendicular  distance  between  this 
and  the  side  opposite : 


COMPUTATIONS  FOR  ENQINEERS.  623 

Rule — Multiply  one  side  by  the  perpendicular  distance  be- 
tween it  and  the  side  opposite : 

or  Area  =  A  D  X  E  F ; 

=  also  A  B  X  G  H. 

Example:    A  D  =  16,  E  F  =  9.     Then  area  =  9  X    16 
:  144. 

[4]  Trapesoid. 

A  trafezoid  is  any  figure,  such  as  A  B  C  D,  having  four 
sides  and  four  angles,  two  of  the  sides,  as  B  C  and  A  D,  being 
parallel. 

AREA,  A  B  C  D.  To  find  the  area  of  a  trapezoid,  having 
given  the  parallel  sides  and  the  perpendicular  distance  between 
them : 

B      E      c 


Rule — Multiply  the  half  sum  of  the  parallel   sides  by  the 
perpendicular  distance  between  them, 


or  Area 


'B  C  +  A  D 


)  X   E  F. 


Example:    B  C=  10,  A  D  =  16,  E  F  =  8.     Then  aiea  = 

-L   l6\ 

)   X  8  =  104. 

[5]  Triangle. 

A  triangle  is  any  figure,  such  as  A  B  C,  having  three  sides 
and  three  angles.     In  a  triangle  placed  as  in  the  figure,  A  C  is 


called  the  base,  and  B  D — the  perpendicular  distance  from  B  to 
A  C — is  called  the  altitude. 

ANY  SIDE,  A  B.     To  find  the  length  of  any  side,  having 
given  the  triangle  complete : 


624  PRACTICAL  MARINE  ENGINEERING. 

Rule — Square  the  other  two  sides  and  add,  and  according 
as  the  angle  between  them  is  greater  or  less  than  90  degrees, 
add  or  subtract  twice  the  product  of  one  of  these  sides  by  the 
projection*  of  the  other  upon  it.  Then  take  the  square  root  of 
the  result  thus  found; 


or 


A  B  =  V  A  C      B  C  -  2  A  C  x  DC. 


Similarly  B  C  =  V  A  B2  +  A  C  2  -  2  A  C  X  A  D, 


C  =  ^~A~B*  +  B~C  +  2  B  C  x  B  E. 
Example:  A  C  =  12,  B  C  =  9,  D  C  =  8.     Then 
A-B  =  ^/  144  +  81  _  2  X  12  X  8  •=  \/~33~=  5-745- 

AREA.  To  find  the  area  of  a  triangle,  having  given  the 
triangle  complete,  or  any  side  and  its  perpendicular  distance 
from  the  opposite  vertex  : 

Rule  —  Multiply  any  side  by  the  perpendicular  distance  from 
the  opposite  vertex  to  such  side  (produced,  if  necessary,  to  meet 
the    perpendicular),    and    take    half    the    product   thus    found; 
or  take  half  the  product  of  the  base  by  the  altitude; 
or  Area  =  y*  (A  C  X  B  D), 
=  y*  (B  C  X  A  E), 
=  y2  (A  B  X  C  F). 

Example:  A  C  =  120,  B  D  =  32.  Then  area  =  %  (120  X 
32)  =  1,920. 

[6]  A  Right-Angled  Triangle. 

In  a  right-angled  triangle  one  of  the  angles,  as  C,  is  a  right 
angle.  The  side  opposite  is  called  the  hypothenuse. 

HYPOTHENUSE,  A  B.  To  find  the  length  of  the  hypoth- 
enuse, having  given  the  other  two  sides  : 

Rule  —  Square  the  other  two  sides  and  add,  and  take  the 
square  root  of  the  sum; 


or 


A  B  =  V  ATC*  +~B~Ca. 


Example  :  A  C  =  9,  B  C  =  1  2.  Then  A  B  =  81  +  144 
=  ^225  =  15. 

SIDE  A  C  or  B  C.  To  find  the  length  of  one  of  the  sides 
about  the  right  angle,  having  given  the  hypothenuse  and  the 
other  side: 


*  Let  B  D  be  drawn  perpendicular  to  A  C.  Then  D  Cis  called  the 
projection  of  B  Cupon  A  C.  Similarly  A  D  is  the  projection  of  A  B  upon 
A  C,  A  .Fthe  projection  of  A  C  upon  A  B  produced,  and  E  C  the  projec- 
tion of  A  Cupon  B  C  produced. 


COMPUTATIONS  FOR  ENGINEERS.  625 

Rule — Square  the  hypothenuse  and  the  given  side.   Subtract 
the  squares,  and  take  the  square  root  of  the  difference ; 


or  A  C  ^       A  If  -  B  C. 
Example:    A    B    =     15,     B    C    =     12.     Then    A     C    = 


225  —   H4  =  v    Bi  =  9» 

AREA,  ABC.    To  find  the  area  of  a  right-angled  triangle, 
having  given  the  two  sides  about  the  right  angle : 

B 


Rule — Multiply  together  the  two  sides  about  the  right  angle, 
and  take  half  their  product ; 

or  Area  =  y2  (A  C  X  B  C). 

Example:  A  C  =  9,  B  C  =  12.  Then  area  =  ^  (9  X 
12)  =  54. 

These  rules  are  special  cases  of  those  for  the  general  tri- 
angle, as  in  [5]. 

[7]  Trapezium. 

A  trapezium  is  a  figure,  such  as  A  B  C  D,  having  four 
angles  and  four  sides,  no  two  of  the  latter  being  parallel. 

AREA,  A  B  C  D.  To  find  the  area  of  a  trapezium,  having 
given  the  figure  complete : 

Rule — Divide  the  trapezium  into  two  triangles,  and  proceed 
with  each  separately,  and  then  add. 


A  **  -  K3  A  *  --- 


[8]  Regular  Polygons. 

A  regular  polygon  is  a  figure,  such  as  A  B  C  D  E,  having 
any  number  of  equal  sides  and  a  like  number  of  equal  angles. 
They  are  named  as  follows  : 


626  PRACTICAL  MARINE  ENGINEERING. 

Number  of  Sides.  Names. 

3  Triangle 

4 Square 

5  Pentagon 

6  Hexagon 

7  Heptagon 

8  Octagon 

9  Nonagon 

10  Decagon 

AREA.  To  find  the  area  of  any  regular  polygon,  as  A  B  C 
D  E,  having  given  the  figure  complete : 

Rule — Divide  the  polygon  into  as  many  triangles  as  there 
are  sides,  the  apexes  all  being  at  the  center.  Find  the  area  of 
one  of  these,  and  multiply  by  the  number  of  sides. 

[9]  Irregular  Figures. 

AREA.  To  find  the  area  of  a  figure,  such  as  A  B  C  D  E  F 
G  having  given  the  figure  complete  : 


— Divide  into  triangles  in  any  convenient  way;   pro- 
ceed with  each  separately,  and  add  the  results. 

[10]  Circle. 

A  circle  is  a  figure  bounded  by  a  curved  line,  every  point 
of  which  is  equally  distant  from  a  point  within,  called  the  center. 
The  distance  across  from  one  side  to  the  other  through  the 
center  is  called  the  diameter  (see  A  B  or  F  G).  The  diameter 
is  usually  represented  by  D.  The  distance  from  the  center  to  the 
curved  boundary  line  is  called  the  radius,  and  is  plainly  one- 
half  the  diameter  (see  A  C,  F  C,  etc.).  The  radius  is  usually 
represented  by  r.  The  curved  boundary  line  A  F  H  B  G  K  A, 
is  called  the  circumference.  Any  part  of  the  circumference,  as 
A  F,  F  H,  etc.,  is  called  an  arc. 


COMPUTATIONS  FOR  ENGINEERS.  627 

CIRCUMFERENCE.  To  find  the  circumference,  having  given 
the  diameter: 

Rule — Multiply  the  diameter  by  3.1416,  or  more  exactly 
by  3.1415927,  or  less  exactly  by  *-f-.  This  ratio  is  frequently 
denoted  by  the  symbol  >r. 

or  Circumference  =  3.1416  X  Diameter  —  ^  D. 

Example:  Diameter  =  n.  Then  circumference  =  n  X 
3.1416  =  34o576. 

DIAMETER.  To  find  the  diameter,  having  given  the  cir- 
cumference : 

Rule — Divide  the  circumference  by  3.1416,  or  more  exactly 
by  3.1415927,  or  less  exactly  by  -2T2-. 

or  Diameter  =  Circumference  -I-  3.1416, 
or  Diameter  —    Circumference     x  -31831. 

Example:  Circumference  =  48.7.  Then  diameter  =  48.7 
-f-  3.1416  =  15.50  + 


AREA,  A  H  B  K.    To  find  the  area  of  a  circle,  having  given 
the  diameter  or  the  radius  : 

Rule — Multiply  the  square  of  the  diameter  by  .7854,  or 
3.1416-7-4. 

or  multiply  the  square  of  the  radius  by  3.1416, 
or  find  half  the  product  of  the  radius  by  the  circumference, 

or  Area  ==    .7854  x  (Diameter)2  —  - 

4 

=  3.1416  x  (Radius)2  =  TT  r\ 
—  J  (Radius  x  Circumference). 

Example:  Diameter  =   10.  Then  area  =   .7854  X    100  = 

78-54- 

,  LENGTH  OF  ARC.  To  find  the  length  of  an  arc,  as  A  F, 
having  given  the  corresponding  number  of  degrees  and  the  cir- 
cumference or  diameter : 

Rule — Divide  the  circumference  by  360,  and  multiply  by  the 
number  of  degrees  in  the  arc ; 


628  PRACTICAL  MARINE  ENGINEERING. 

or  multiply  the  number  of  degrees  by  .008727  and  the  product 
by  the  diameter, 

_      Circumference  r 

or  Length  A  F  =  -      — ,-—          X  (Number  of  Degrees) 

or  Length  A  F  =  (Number  of  Degrees)  X  .008727  X  Diameter. 
Example:     Find  the  length  of  an  arc  of  60  degrees  in  a 
circle  whose  diameter  is  20. 

Length  =  60  X  .008727  X  20  =  10.4724. 

[n]  Circular  Ring  or  Annulus. 

The  surface  lying  between  two  circles,  as   shown  by  the 
shaded  part  of  the  figure,  is  called  a  circular  ring  or  annulus. 


AREA.  To  find  the  area  of  a  circular  ring,  having  given  the 
radii  of  the  two  circles : 

Rule- — Find  the  difference  between  the  areas  of  the  two 
circles, 

or  Area  =  3. 1416 1J7T-- 3.141670    ==  3.1416  (U~B  -  OA2.) 

[13]  Sector  of  Circle. 

The  surface  lying  between  two  radii  and  the  corresponding 
part  of  the  circumference,  as  shown  by  the  shaded  part  of  the 
figure,  is  called  the  sector  of  a  circle,  or  a  circular  sector. 

A 


AREA,  ABO.  To  find  the  area  of  the  sector  of  a  circle, 
having  given  the  corresponding  number  of  degrees  and  the 
diameter: 

Rule — Find  the  area  of  the  entire  circle,  divide  by  360,  and 
multiply  by  the  number  of  degrees  in  the  sector; 


COMPUTATIONS  FOR  ENGINEERS.  629 

Area  of  Circle  ,. 
or  Area  =  -     — -   (Number  of  Degrees  in  Sector) ; 

or,  by  proportion,  360°    :  Number  of  Degrees  in  Sector     :     : 

Area  of  Circle :  Area  of  Sector; 
or,  otherwise,  find  half  the  product  of  the  arc  by  the  radius, 

or  Area  =  y2  (O  A  X  A  B). 

Example:  Find  the  area  of  a  sector  of  60  degrees  in  a  circle 
whose  radius  is  10. 

Area  of  entire  circle  =  78.54, 

hence  Area  =  l—£$  x  60  =  Ljl*  _i  3.09. 
360  6 

[13]  Segment  of  Circle. 

A  line,  such  as  A  B,  cutting  across  a  circle  is  called  a  chord. 
A  part  of  the  surface  of  a  circle  between  a  chord  and  the  cir- 
cumference, as  shown  by  the  shaded  part  of  the  figure,  is  called 
a  segment  of  a  circle. 

C 
%»>. 

B 


AREA,  A  C  B.  To  find  the  area  of  the  segment  of  a  circle, 
having  given  the  angle,  A  O  B,  and  the  diameter  or  radius  of 
the  circle : 

Rule — Find  the  area  of  the  sector,  O  A  C  B,  as  in  [12],  and 
of  the  triangle  O  A  B,  as  in  [5],  and  subtract  the  latter  from  the 
former, 

or  Area  =  %  (A  C  B  X  O  A  —  O  E  X  A  B). 

Example:  O  A  =  10,  O  E  =  5,  A  B  =  17.32,  A  C  B 
=  20.944, 

then  Area  —  */2  (20.944  X  10  —  5  X  17.32)  =  61.42. 

[14]  Ellipse. 

If  the  surface  of  a  circle,  as  shown  by  the  dotted  line,  be 
uniformly  stretched  in  one  direction  (horizontal  in  the  figure) 
until  the  diameter,  A,  B,,  becomes  equal  to  A  B,  the  circum- 
ference will  be  changed  into  a  curved  line,  A  C  B  D,  and  the 
figure  thus  formed  is  called  an  ellipse.  The  two  lines,  A  B  and 
C  D,  are  called  the  diameters  of  the  ellipse. 


<63o  PRACTICAL  MARINE  ENGINEERING. 

AREA,  A  C  B  D.     To  find  the  area  of  an  ellipse,  having 
.given  the  two  diameters : 


Rule — Multiply  the  product  of  the  two  half  diameters  by 


or  Area  =  3.1416  X  O  C  X  O  B. 

Example:  O  C  =  5,  O  B  =  8.  Then  area  =  3.1416  X  5 
X  8  =  125.664. 

[15]  Figures  With  an  Irregular  Contour. 

To  find  AREA,  A  B  C  D,  representing,  for  example,  an  indi- 
cator card.  This  cannot  be  done  with  absolute  exactness,  but 
there  are  a  number  of  rules  for  finding  the  approximate  area 
as  closely  as  we  may  desire. 


Divide  the  base  O  X  into  any  appropriate  number  of  in- 
tervals, usually  10  for  an  indicator  card,  and  draw  lines  across 
the  card  as  shown. 

Rule  (i) — (Trapezoidal).  Measure  the  successive  ordinates 
or  breadths  on  the  full  line  and  from  their  sum  subtract  one- 
half  the  sum  of  the  end  ordinates.  Multiply  the  remainder  by 
the  length  of  the  interval  or  by  O  X  -^  10,  and  the  product  is  the 
area  desired; 

or  calling  the  breadths   y0,  y^  J2,    etc.,  we  have  by  formula  in 
this  case. 


COMPUTATIONS  FOR  ENGINEERS.  631 

Area  =  —  (  J  y0  +  yt  +  j/a  +  j/3  +  j/4  +  jr.  +  y<  +  J7  +  /8  +  y9  + 


As  a  slightly  different  and  preferable  mode  of  procedure 
with  this  rule  we  may  measure  the  breadths  midway  between 
the  lines  of  division  as  indicated  by  the  dotted  lines.  Their  sum, 
without  modification,  is  then  multiplied  by  the  length  of  the  in- 
terval as  before. 

Any  number  of  spaces  as  desired  may  be  employed  with 
this  rule. 

Rule  (2)  —  (Simpson  s  or  Parabolic).  Measure  the  ordinates 
as  before. 

Take  :  Once  the  first  and  last.  Four  times  every  other  one 
beginning  with  the  second.  Twice  the  remaining. 

(These  multipliers  are  shown  in  the  figure  below  the  line 
O  X.) 

Add  the  products  and  multiply  by  one-third  the  interval, 
or  in  this  case  by  O  X  -4-  30  ;  or  by  formula  in  this  case  : 
n  x 

Area  =  —  -~  (yQ  +  4j>,  +  zj2  +  4/3  +   zj/4  +  4js  +  2j6  +  47,  + 


With  this  rule  the  number  of  spaces  must  be  even. 

Rule  (3)  —  (Durand's).    Measure  the  ordinates  as  before.   To 
their  sum  add  one-twelfth  the  sum  of  those  next  the  end  and 
subtract  seven-twelfths  of  those  at  the  end.     Multiply  the  result 
by  the  interval  and  the  product  is  the  area  desired  ; 
or  by  formula  in  this  case  : 


With  this  rule  any  number  of  spaces  as  desired  may  be  em- 
ployed. 

The  measurement  and  addition  of  ordinates  as  in  rules  (i) 
and  (3)  may  be  quickly  effected  by  means  of  a  strip  of  paper  on 


which  their  lengths  are  marked  off  directly  from  the  card  and 
without  the  use  of  a  scale,  joining  the  end  of  one  to  the  be- 
ginning of  the  next  and  thus  effecting  mechanically  the  addi- 
tion desired. 


632  PRACTICAL  MARINE  ENGINEERING. 

To  a  reduced  scale  the  strip  when  marked  would  resemble 
the  figure,  the  ordinates  being  as  indicated  on  the  margin.  The 
sum  total  is  then  directly  found  by  means  of  a  scale. 

Example:  Suppose  that  the  ordinates  of  an  irregular  area 
at  one-half  inch  intervals  are  found  by  measurement  to  be  as 
follows  in  column  (i)  : 


fl) 

(2) 

(3) 

—  Ordinates.  > 

Multipliers. 

Products. 

Jo                                           -44 

i 

•44 

y, 

.42 

4 

5.68 

y. 

.61 

2 

3.22 

73 

.56 

4 

6  24 

^4 

•51 

2 

3.02 

?* 

.46 

4 

5-84 

^6 

.  20 

2 

2.40 

y7                -95 

4 

3.80 

Js                               .71 

2 

1.42 

y9                -49 

4 

1.96 

y»              .18 

i 

.18 

Sums  11.53  34-20 

We  then  have,  according*  to  rule  (i)  : 

Sum  of  ordinates  =   11.53 


Difference....    •=.  11.22 
Interval =       .5 


Area   =   Product   =     5.61  square  inches. 
According  to  rule  (2),  we  have  the  multipliers  and  products 
as  given  in  columns  (2)  and  (3). 
We  then  have : 

Area  =  YZ  X  -5  X  34-2O  =  5.70  square  inches. 
According  to  rule  (3),  we  have  from  column  (i)  : 

Sum  of  ordinates =   H-53 

TV  sum  of  next  to  ends  =       .16 


Sum =   11.67 

sum  of  ends —       .36 


Difference =   11.31 

A'rea  =  .5  X  11.31  =  5-66  square  inches. 


COMPUTATIONS  FOR  ENGINEERS. 


633 


Areas  of  irregular  figures,  such  as  indicator  cards,  etc.,  may 
also  be  found  by  an  instrument  called  the  planimeter.  In  this 
instrument  a  pointer  is  traced  around  the  contour  of  the  figure, 
while  the  area  is  read  off  from  a  wheel,  which  is  given  appro- 
priate motion  by  the  movement  of  the  pointer.  Such  instru- 
ments, with  instructions  for  use,  may  usually  be  obtained  from 
the  makers  of  steam-engine  indicators  or  from  dealers  in  mathe- 
matical instruments. 

[16]  Prism. 

A  prism  is  a  solid  body,  bounded  by  two  equal  and  parallel 
ends  and  by  three  or  more  sides  or  faces,  forming  at  their  junc- 
tion a  like  number  of  parallel  edges. 

iWhen  the  sides  are  perpendicular  to  the  ends,  and  are 
therefore  all  rectangles,  the  solid  is  known  as  a  right  prism. 

When  the  sides  and  ends  are  all  square,  the  solid  is  known 
as  a  cube. 

K  F  r* 


M 


H 


SURFACE.  To  find  the  surface  of  any  prism,  having  given 
the  figure  complete : 

Rule — Find  the  area  of  the  base  (or  top)  by  such  of  the 
preceding  rules  as  may  be  appropriate.  For  the  side  or  lateral 
surface,  multiply  the  perimeter  or  boundary  of  the  base  by  the 
perpendicular  or  shortest  distance  between  any  two  correspond- 
ing lines  of  the  base  and  top  (as  K  L  in  Fig.  a). 

VOLUME.  To  find  the  volume  of  any  prism,  having  given 
the  base  and  altitude : 

Rule — Multiply  the  area  of  the  base  or  end  by  the  altitude 
or  perpendicular  distance  between  the  two  ends. 

RIGHT  PRISM.  In  a  right  prism  the  preceding  general  rules 
hold,  but  the  lateral  faces  are  all  rectangles,  and  the  perpen- 
dicular distance  between  their  ends,  as  K  L ;  the  length  of  an 
edge,  as  M  N,  and  the  altitude  or  perpendicular  distance  be- 
tween the  ends,  all  three  become  equal. 


634 


PRACTICAL  MARINE  ENGINEERING. 


RIGHT  PRISM,  WITH  RECTANGULAR  BASE.  In  a  solid  of 
this  character  (see  Fig.  b)  the  preceding1  rules  still  hold,  but  the 
sides  and  ends  are  all  rectangles,  and  the  rules  may  be  simplified 
as  follows : 

For  the  LATERAL  SURFACE  : 

Rule — Multiply  the  perimeter  of  the  base  by  the  altitude, 
or  Lateral  Surface  =  Length  ABCDAXAE. 

For  the  VOLUME  : 

Rule — Multiply  together  the  length  and  breadth  of  base  and 
the  product  by  the  altitude, 

or  Volume  =  ABXADXAE. 

Example:  AB  =  8,  AD  =  6,  AE  =  10.  Then  lateral 
surface  =  (8  +  6  +  8  +  6)  X  10  =  28  X  10  =  280,  and 
volume  =  8  X  6  X  ip  =  480. 

[17]  Cylinder. 

A  solid  with  a  circular  cross  section  of  constant  size  is  called 
a  cylinder.  If  the  center  of  the  top  is  vertically  over  the  center  of 
the  base,  the  solid  is  called  a  right  cylinder. 


LATERAL  SURFACE  OF  RIGHT  CYLINDER.  To  find  the  lateral 
surface  of  a  right  cylinder,  having  given  the  diameter  of  base 
and  the  altitude : 

Rule — Multiply  the  circumference  of  the  base  by  the  altitude, 
or  Lateral  Surface  =  Circumference  A  B  C  D  X  A  E  =  3.1416 
X  A  C  X  A  E. 

Example:  A  C  =  10,  A  E  =  20.  Then  lateral  surface  = 
3.1416  X  10  X  20  =  628.32. 

VOLUME  OF  RIGHT  CYLINDER.  To  find  the  volume  of  a 
right  cylinder,  having  given  the  base  and  altitude : 

Rule—  Multiply  the  area  of  the  base  by  the  altitude, 
or  Volume  =  Area  ABCDXAE=  .7854  ATC  X  A  E. 


COMPUTATIONS  FOR  ENGINEERS. 


635 


Example:    A  C  =  10,  A  E  =  20. 
100  X  20  =  1,570.8. 


Then  volume  =  7854  X 


[18]   Any  Solid  With  a  Constant  Section  Parallel  to  the  Base, 
Either  Right  or  Oblique. 

Such  a  solid  is  the  general  case  of  which  the  prism  and 
cylinder  are  but  special  examples.  The  rules  will  therefore  be 
similar  to  those  of  [16]  and  [17]. 

SURFACE.  To  find  the  surface  of  such  a  solid,  having  given 
the  figure  complete : 

Rule — Find  the  area  of  the  base  (or  top)  by  such  of  the  pre- 
ceding methods  as  may  be  appropriate.  For  the  side  or  lateral 
surface,  multiply  the  perimeter  or  boundary  of  the  base  by  the 
perpendicular  or  shortest  distance  between  any  two  correspond- 
ing lines  of  the  base  and  top  (as  K  L  in  figure  a) : 

or  Lateral  Surface  =  Length  ABCDEAXKL. 


A\ 


VOLUME.    To  find  the  volume  of  such  a  solid,  having  given 
the  figure  complete : 

Rule — Multiply  the  area  of  the  base  by  the  perpendicular 
distance  between  the  base  and  the  top. 

or  Volume  =  Area  of  Base  X  Vertical  Altitude. 

Example:  Area  of  base  =-  120,  altitude  =  40.    Then  volume 

=   40    X     120    =-    4,800. 

[19]  Wedge. 

A  right  prism  with  a  triangular  base,  as  in  b  above,  having 
two  sides  equal,  as  A  C  and  B  C,  is  called  a  wedge. 

To  find  the  SURFACE  or  VOLUME,  use  the  same  rules  as 
in  [16]. 

[20]   Right  Pyramid. 

A  solid,  bounded  by  a  base  and  by  triangular  sides  meeting 
in  a  point  or  apc.v,  as  P,  is  called  a  pyramid.     If  the  base  is  a 


636 


PRACTICAL  MARINE  ENGINEERING. 


regular  polygon  [8]  and  the  apex  is  vertically  over  the  center 
of  the  base,  the  solid  is  called  a  right  pyramid  (see  figure  a 
below). 

LATERAL  SURFACE.  To  find  the  lateral  surface  of  a  right 
pyramid,  having  given  the  figure  complete : 

Rule — Take  one-half  the  product  of  the  perimeter  or  bound- 
ary of  the  base  by  the  perpendicular  or  shortest  distance  from 
the  apex  to  one  of  the  sides  of  the  base,  as  P  F, 

Length  ABODE  A  x  PF 
or  Lateral  Surface  =  - 

2 

VOLUME.  To  find  the  volume  of  a  right  pyramid,  having 
given  the  base  and  altitude : 

Rule — Take  one-third  of  the  product  of  the  area  of  the  base 
by  the  altitude,  as  P  O, 

(Area  of  Base)  x  (Altitude) 
or  Volume  =  J 


Engineering 


Example:     Area   of 
i 80  X  16 


base   =    180,   altitude   =    16.     Then 


volume  — 


3 


=   QOO. 


General  Pyramid. 

For  definition  see  [20],  also  Fig.  b  above. 

LATERAL  SURFACE.  To  find  the  lateral  surface  of  any 
pyramid,  having  given  the  figure  complete : 

Rule — The  surface  will  consist  of  a  series  of  triangles,  simi- 
lar or  not,  according  to  the  nature  of  the  pyramid.  These  must 
be  computed  according  to  the  rules  for  triangles  and  the  re- 
sults added. 

VOLUME.  To  find  the  volume  of  any  pyramid,  having  given 
the  base  and  altitude : 

Rule — Take  one-third  the  product  of  the  area  of  the  base  by 
the  vertical  altitude,  as  G  H, 


COMPUTATIONS  FOR  ENGINEERS.  637 

(Area  of  Base)  x  G  H 
or  Volume  =  — 

3 
Example:    Area  of   base  =  48,   G  H  —   18.        Then  vol- 


ume   =  =  288. 

3 

[22]  Right  Circular  Cone. 

Any  solid  having  a  base  with  curved  or  irregular  boundary, 
an  apex,  and  straight  sides,  is  called  a  cone  in  general.  If  the 
base  is  a  circle  and  the  apex  is  vertically  over  the  center,  the 
solid  is  called  a  right  circular  cone  (see  figure). 

LATERAL  SURFACE.  To  find  the  lateral  surface  of  a  right 
circular  cone,  having  given  the  base  and  the  slant  height  : 

Rule  —  Take  one-half  the  product  of  the  circumference  of 
the  base  by  the  slant  height, 

Circumference  ABC  D  A  x  A  £ 
or  lateral  surface    =     -  —  - 


Example:    Diameter  =  10,  A  E  =  20.     Then  surface  = 

3.1416  X  10  X  20 

,  -  =314.16. 

VOLUME.  To  find  the  volume  of  a  cone,  having  given  the. 
base  and  altitude  : 

Rule  —  Take  one-third  the  product  of  the  area  of  the  base  by 
the  altitude, 

Area  of  Base  A  B  C  D  X  E  F 
or  volume  =  __  _  _  _ 

3 
Example:    Diameter  =   8,  E  F  =    15.    Then  volume  = 


3 

[23]  General  Cone. 

For  definition  see  [22]  . 

VOLUME.    To  find  the  volume  of  any  cone,  having  given  the 
base  and  vertical  altitude  : 


638  PRACTICAL  MARINE  ENGINEERING. 

Rule — Take  one-third  the  product  of  the  area  of  the  base  by 
the  vertical  altitude,  as  -F  G, 

Area  of  base  X  F  G 
or  volume  =  _ 


Example:  Area  of  base  =  240,  F  G  —  40.  Then  volume  = 
240  X  40 

_=   £200. 

[34]  Frustum  of  Right  Pyramid. 

The  solid  contained  between  the  base  of  a  pyramid  and  a 
parallel  plane,  as  E  F  G  H,  is  called  the  frustum  of  a  pyramid. 

LATERAL  SURFACE.  To  find  the  lateral  surface  of  a  frustum 
of  a  right  pyramid,  having  given  the  figure  complete : 

Rule — Add  the  perimeters  or  boundaries  of  the  base  and  top, 
and  multiply  the  sum  by  one-half  the  perpendicular  or  shortest 
distance  between  two  corresponding  lines  of  the  base  and 
top,  which  we  may  denote  by  h. 


or  lat.  surface  -  (length  A  B  C  D  +  length  E  F  G  H}  X  h 

2 

Example:  A  B  =  10,  A  D  =  12,  E  F  =  6,  E  H  =  7.2,  k 
=    .    Then  surface  =  (44  +  *M)  X  5  = 


5 

2 

VOLUME.  To  find  the  volume  of  a  frustum  of  a  right  pyra- 
mid, having  given  the  base  and  top  and  vertical  distance  be- 
tween them  : 


COMPUTATIONS  FOR  ENGINEERS,  639 

Rule  —  Add  together  the  areas  of  the  base  and  top  and  the 
square  root  of  their  product,  and  multiply  the  sum  by  one-third 
the  vertical  altitude,  which  we  may  denote  by  k, 


orvol  __(ABCD  +  EFGH  +  [/AB  C  DyEFG  H)  X  k 

3 
Example:  Area  A  B  C  D  =  100,  area  E,  F  G  H  =  42,  k  = 

rr,  (100  +  42  +  I/  4,200)  X  12       0 

12.    Then  volume  =  v  _  Z  _  —  _  _  _    =  827.2. 

3 

[25]  Frustum  of  General  Pyramid,  as  [21]. 
To  find  the  LATERAL  SURFACE  : 

Rule  —  The  surface  will  consist  of  a  number  of  trapezoids, 
similar  or  not,  according  to  the  nature  of  the  frustum.     These 
must  be  computed  according  to  [4]  and  the  results  added. 
To  find  the  VOLUME  : 
Rule  —  Same  as  for  [24]. 

[26]  Frustum  of  Right  Cone. 

The  solid  contained  between  the  base  of  a  cone  and  a  parallel 
plane,  as  E  F  G  H,  is  called  the  frustum  of  a  cone. 


LATERAL  SURFACE.  To  find  the  lateral  surface  of  a  frustum 
of  a  right  cone,  having  given  the  base  and  top  and  slant  height : 

Rule — Add  the  circumference  of  the  base  and  top,  arid  mul- 
tiply the  sum  by  one-half  the  slant  height,  as  A  E, 

or  lat.  surface  =  «*•  A  B  C  D  +  C«.E  F  G  H)-*A>E 

2 

Example:  Diameter  A  Ct=  12,  diameter  E  G  =  10,  A  E  =  8. 
Then  surface  =  (3-i4i6  X  12  +  3.1416  X  10)  X  8_ 

2 

VOLUME.     To  find  the  volume  of  a  frustum  of  a  right  cone, 
having  given  the  base  and  top  and  vertical  altitude : 
Rule — Same  as  for  [24] . 
Or  in  slightly  different  form,  we  have  the  following : 


640  PRACTICAL  MARINE  ENGINEERING. 

Rule— Add  together  the  square  of  the  upper  diameter,  the 
square  of  the  lower  diameter,  and  their  product,  and  multiply  the 
sum  by  the  vertical  altitude  and  by  the  number  .2618, 

or  volume  =  .2618  /  7  (ETG'-j-^TC'-f  E  G  X  A  C). 
Example:  E  G  =  6,  A  C  =  8,  I  J  =  4.     Then  volume  = 
.2618  X  4  (36  +  64  +  48)  =  155. 

[27]  Frustum  of  General  Cone,  as  [23]. 

To  find  the  VOLUME  : 
Rule — Same  as  for  [24]. 

[28]  Sphere. 

A  solid  inclosed  by  a  curved  surface,  every  point  of  which 
is  equally  distant  from  a  point  within  called  the  center,  is  called  a 
sphere.  The  distance,  A  B,  from  one  side  to  the  other  through 
the  center  is  called  the  diameter.  The  distance,  A  0,  from  the 


surface  to  the  center  is  called  the  radius,  and  is  plainly  one-half 
the  diameter. 

SURFACE.    To  find  the  surface  of  a  sphere,  having  given  the 
diameter : 

Rule — Square  the  diameter  and  multiply  by  3.1416, 

or  Surface  =  3.1416  (Diameter)2. 

Example:    Diameter  =  20.    Then  surface  =  3.1416  X  400 
=  1,256.64. 

VOLUME.    To  find  the  volume  of  a  sphere,  having  given  the 
diameter  or  radius : 

Rule — Multiply  the  cube  of  the  radius  by  4.1888, 
or  multiply  the  cube  of  the  diameter  by  .5236, 
or  volume  =  4.1888  A  O3. 
or  volume  =     .5236  A  B3. 

[29]  Volumes  of  Irregular  Shape. 

Volumes  of  irregular  shape  in  which  the  areas  of  a  series  of 
equally-spaced  sections  may  be  found. 


COMPUTATIONS  FOR  ENGINEERS. 


641 


Rule — Find  the  areas  of  a  series  of  equally-spaced  cross  sec- 
tions and  treat  them  by  the  rules  given  in  [15],  using  areas  for 
ordinates.  The  result  will  give  the  volume  desired. 

Examples: 

(1)  Find  the  volume  of  an  irregular  box,  12  feet  long;  area, 
of  one  end,  6  square  feet;  of  the  other,  15  square  feet,  and  of  a 
section  midway  between,  10  square  feet.    The  interval  is  6  feef. 

Then  with  Simpson's  rule, 

Volume  =  2  X  (&  +  4  X  10  +  15)  =  122  cubic  feet. 

(2)  Find  the  volume  of  a  coal  bunker,  20  feet  long,  having, 
cross  sections  every  4  feet,  as  follows : 

Taking  rule  (3),  in  [15],  we  find  the  result  as  below: 

297 

8-3 

305.3 

554 

249.9 
4 

999.6;  or,  say,  1,000  cubic  feet. 


A_    = 


Sum     = 


[30]  Volume  Generated  by  Any  Area  Revolving  About  an  Axis. 

To  find  the  surface  or  volume  of  such  a  body,  the  so-called 
"Rules  of  Pappus"  are  most  readily  applicable.    These  may  be 


642  PRACTICAL  MARINE  ENGINEERING. 

illustrated  by  the  example  of  the  Torus  or  Ring  as  in  the  figure. 

SURFACE.  To  find  the  surface  of  a  ring,  having  given  the 
necessary  dimensions : 

Rule — Multiply  the  length  of  the  generating  line  by  the 
length  of  the  path  followed  by  its  center  of  gravity. 

Example,  as  in  the  figure. 

The  length  of  the  generating  line  is  2  TT  r. 

The  length  of  the  path  of  the  center,  C,  is  2  K  a. 

The  surface  is.-.  2  TT  r  x  2  TT  a  =  4  x2  a  r 

VOLUME.  To  find  the  volume  of  a  ring,  having  given  the 
necessary  dimensions : 

Rule — Multiply  the  generating  area  by  the  length  of  the  path 
traveled  by  its  center  of  gravity. 
.    Example,  as  in  the  figure. 

The  generating  area  is  n  r2. 

The  length  of  the  path  of  the  center,  C,  is  2  n  a. 

The  volume  is  .-.  2  x2  a  r*. 

The  same  general  rules  apply,  no  matter  what  the  form  of 
the  generating  area,  and  they  will  often  be  found  of  use  in  solving 
problems  not  readily  treated  in  any  other  manner. 

Sec.  10.  PROBLEMS  IN  GEOMETRY. 

[i]  At  Any  Point  in  a  Straight  I<ine  to  Erect  a  Perpendicular. 

Let  0  be  the  given  point  in  the  line  L  M.  Then  take  points 
A  and  B  such  that  0  A  —  0  B.  From  A  and  B  as  centers  with 

E 
CC 

G 


LA 


B     M 
'D 


any  radius  greater  than  A  0  or  0  B,  describe  arcs  cutting  in 
C  or  D,  or  if  preferred,  in  both.  Then  a  line  drawn  through  0 
and  C  or  0  and  D  will  be  perpendicular  to  L  M,  or  the  line  may 
be  drawtt  through  C  and  D,  in  which  case  it  will  also  contain  0 
and  be  perpendicular  to  L  M  as  before. 


COMPUTATIONS  FOR  ENGINEERS.  643 

[«]  To  Bisect*  the  Distance  Between  Two  Points. 

In  the  figure  for  problem  [i]  let  A  and  B  be  the  two  points. 
Then  finding  points  C  and  D  as  in  [i]  it  is  plain  that  the  point 
0  determined  by  drawing  the  line  C  D  will  be  the  middle  point 

between  A  and  B  as  desired,  and  that  we  shall  have  A  0  =  0  B. 

i 

[3]  To  Find  the  Center  from  Which  to  Pass  an  Arc  of  Given 
Radius  Through  Two  Given  Points. 

In  the  figure  for  problem  [i]  let  A  and  B  be  the  points. 
Then  finding  points  C  and  D  as  in  [i]  it  is  plain  that  any  point 
in  the  indefinite  line  E  F  will  be  at  equal  distances  from  A  and  B. 
Hence  from  A  or  B  as  a  center  and  with  the  given  radius  cut  the 
line  E  F  in  a  point  as  G.  This  is  the  point  desired. 


2345 


[4]  To  Divide  a  Given  I/ine  Into  a  Given  Number  of  Equal  Parts. 

Let  A  B  denote  the  given  line.  Draw  a  line  A  D  at  a  small 
angle  with  A  B,  and  lay  off  upon  it  as  many  equal  divisions  A  a, 
a  b,  b  c,  etc.,  as  it  is  desired  A  B  shall  have.  These  divisions 
should  be  so  chosen  that  the  total  length  A  f  shall  not  widely 
differ  from  A  B.  Next  draw  B  f  and  then  a  series  of  parallels 
through  the  points  of  division  a  b  c,  etc.  The  points  where  these 
lines  cut  A  B  will  give  the  points  of  division  desired. 


B  A 

[5]  To  Construct  a  Triangle,  Having  Given  the  Three  Sides. 

Let  a  b  c  denote  the  sides.    Take  A.  B  =  c,  and  from  A  as 


*  To  bisect  a  geometrical  quantity  means  to  divide  it  into  two  equal 
parts. 


644 


PRACTICAL  MARINE  ENGINEERING. 


center  and  with  b  as  radius,  describe  an  arc  D  E,  and  similarly 
from  B  as  center  and  with  a  as  radius  describe  an  arc  F  G.  These 
arcs  intersect  in  C,  and  drawing  lines  A  C,  B  C,  the  construction 
is  completed. 

[6]  To  Bisect  a  Qiven  Arc  or  Angle. 

Let  A  0  B  denote  the  angle  and  A  B  the  arc.  From  A  and 
B  as  centers,  and  with  any  radius  greater  than  half  the  distance 
between  A  and  B,  describe  arcs  intersecting  in  some  point  C. 
Then  a  line  0  C  will  bisect  the  angle  A  0  B  and  at  D  the  arc 
AB. 


[7]  To  Construct  a  Mean  Proportional*  Between  Two  Given 

I<ines. 

Let  the  two  lines  be  denoted  by  A  B  and  B  C  placed  end  to 
end.  Find  the  center  0  of  the  line  A  C,  and  describe  a  semi-circle 
ADC.  Draw  B  E  at  right  angles  to  A  C.  Then  B  E  is  the 
desired  mean  proportional,  and  wre  have  : 

AB  :BE  :  :  B  E  :  B  C 


or,  A  B  X  B  C  —  B  £2 

[8]  To  Construct  a  Fourth  Proportional!  to  Three  Given  I/ines. 

Let  a,  b  and  c  denote  the  three  lines,  and  let  the  desired  pro- 
portion be  : 

a  :b  :  :c  : 


*  A  mean  proportional  between  two  quantities  a  and  c  is  a  third  quan- 
tity 6,  such  that  we  have  : 

a  :  b  ::  b  :  c 
or,     £2  —  a  c 
or,     b  —  v/  a  c. 
See  also  Sec.  6. 

t  A  fourth  proportional  to  three  quantities  a,  b  and  c  is  a  quantity  d, 
such  that  we  have  : 

a  :  b  :  :  c  :  d. 
See  also  Sec.  6. 


COMPUTATIONS  FOR  ENGINEERS.  645 

Lay  off  A  B  —  a  and  A  C  =  b.  Then  at  any  convenient 
angle  lay  off  A  K  and  take  on  it  a  distance  A  D  —  c.  Draw  B  D 
and  C  E  parallel  to  it.  Then  A  E  is  the  fourth  term  desired  and 
we  have : 


B 5" 

A  B  :A  C  :  :  A  D  :  A  E 


[91  To  Construct  a  Square  Equivalent  in  Area  to  a  Given 

Rectangle. 

Find  by  problem  [7]  a  mean  proportional  between  the  sides 
of  the  rectangle,  and  this  will  be  the  side  of  the  square  desired. 

[10]  To  Construct  a  Square  Equivalent  in  Area  to  a  Given 

Triangle. 

Find  by  problem  [7]  a  mean  proportional  between  the  base 
and  half  the  altitude,  or  between  the  altitude  and  half  the  base. 
This  will  be  the  side  of  the  square  desired. 

[n]  With  One  Given  Side,  to  Construct  a  Rectangle  Equiva- 
lent to  a  Square. 

This  is  equivalent  in  [7]  to  having  given  A  B  the  side  of  the 
rectangle  and  B  E  the  side  of  the  square.  Find  by  the  use  of  the 
construction  in  problem  [i]  a  point  0  on  A  B  at  equal  distances 
from  A  and  E  and  describe  the  semi-circle.  Then  B  C  is  tHe 
remaining  side  of  the  rectangle  desired. 

[12]  To  Find  the  I/ength  of  an  Arc  of  a  Curve. 

Let  A  C  D  B  denote  the  given  arc.  Take  a  strip  of  paper 
M  N  and  lay  with  an  edge  just  neatly  tangent  to  the  curve  at  A. 
Mark  a  point  opposite  A  on  the  strip.  Then,  placing  the  pencil 
at  C,  a  point  near  where  the  curve  and  edge  of  the  paper  strip 
begin  to  separate,  bear  down  slightly  and  rotate  the  paper  about 
C  as  a  center  until  the  edge  is  tangent  at  C  or  at  a  point  slightly 
beyond.  Then  move  the  pencil  along  to  a  point  D  and  repeat, 
and  so  on  until  the  strip  has  been  thus  rolled  along  the  curve  to 


646 


PRACTICAL  MARINE  ENGINEERING. 


B.  The  distance  Ai  J5i,  between  the  point  opposite  A  on  the  strip 
at  the  start  and  the  point  opposite  B  at  the  end,  will  be  very  close 
to  the  true  length  of  the  curve.  A  little  experience  will  enable 
the  points  C  D,  etc.,  to  be  so  chosen  that  the  error  will  be  very 
small.  A  check  on  the  operation  may  be  obtained  by  reversing 


the  process  and  rolling  the  paper  back  to  the  original  position. 
If  the  point  A*  comes  again  to  A  it  shows  that  no  slip  has  been 
made,  and  the  distance  found  may  be  accepted  as  a  very  close 
approximation  to  the  true  length  of  the  curve. 

[13]  To  Construct  an  Ellipse. 

Of  the  many  methods  available,  three  are  given  as  follows : 

(i)  Given  the  two  diameters  A  B  and  C  D.    Take  B  Q  equal 

to  0  C  and  then  0  P  equal  to  0  Q.    Draw  P  Q  and  find  R  its 

middle  point.    Then  take  Q  H  =  Q  R,  and  0  E,  0  F,  0  G  all 


equal  0  H.  Through  E,  F,  G  and  H  draw  lines  as  shown. 
Then  with  H  and  F  as  centers  draw  arcs  /  K  and  /  L,  and  with 
E  and  G  as  centers  draw  arcs  L  K  and  /  /.  These  arcs  join  and 
complete  the  contour.  While  this  method  is  only  approximate 
and  does  not  give  a  true  ellipse,  it  answers  very  well  for  draught- 
ing purposes  where  a  good  representation  of  an  ellipse  is  all  that 
is  desired. 

(2)  This  method  is  exact  in  principle.  Given  A  B  and  C  D 
the  two  diameters  as  before.  With  C  as  center  and  C  Q  =  0  B 
as  a  radius  find  the  points  P  Q.  These  are  the  foci  of  the  ellipse. 


COMPUTATIONS  FOR  ENGINEERS. 


647 


Then  adjust  a  thread  P  C  Q  secured  at  P  and  Q  and  of  a  length 
PC-\-CQ  =  AB.  A  pencil  carried  around  in  the  bight  of  this 
thread,  as  shown  in  different  positions  at  E,  C,  F,  will  trace  the 
ellipse  desired. 

|Y 

c  C- 


(3)  This  method  is  also  exact  in  principle.  Given  A  B  and 
C  D  the  two  diameters  as  before.  Prepare  a  strip  of  cardboard 
or  thin  wood  with  holes  P,  B,  Q,  such  that  P  B  equals  one-hall 
A  B  and  B  Q  equals  one-half  C  D.  Then  move  the  trammel,  as  it 
is  called,  so  that  P  shall  always  move  on  the  vertical  Y  Y  and  Q 
on  the  horizontal  X  X.  The  point  B  will  then  trace  the  ellipse 
desired.  If  points  on  the  curve  only  are  required,  this  method 
is  readily  applied. 

[14]  To  Construct  Any  Regular  Polygon  (Approximate). 

Let  A  B  denote  any  diameter  of  the  given  circle  within 
which  the  polygon  is  to  be  inscribed.  Divide  A  B  into  as  many 
parts  as  there  are  to  be  sides  in  the  polygon.  From  A  and  B  as 


centers  and  radius  A  B  describe  arcs  cutting  in  D.  From  D  draw 
a  line  D  C  through  the  second  of  the  points  of  division.  Then 
B  C  is  the  side  of  the  polygon  desired  within  a  very  small  error. 
For  the  square  or  hexagon,  or  when  the  number  of  sides  is  4  or  6, 
the  construction  is  exact. 


648 


PRACTICAL  MARINE  ENGINEERING. 


[15]  To  Develop  the  Surface  of  a  Cylinder. 

Let  A  B  C  D  denote  the  cylinder.  Lay  off  E  F  =  the  alti- 
tude and  E  H  =  the  circumference  of  the  base,  =  71  X  diam. 
='  3.1416  X  diam.  Then  the  rectangle  E  F  G  H  represents  the 
development  desired. 


H 


[16]  To  Develop   the  Surface   of  a  Cylinder   Which   is  Inter- 
sected by  Another  Cylinder,  the  Two  Axes 
Being  in  the  Same  Plane. 

The  developed  form  of  the  intersection  is  the  only  part 
requiring  special  notice.  Let  A  B  C  D  and  E  F  G  H  denote  the 
two  cylinders.  Draw  any  line  T  T  to  denote  the  element  C  D 
in  the  developed  surface  of  A  B  C  D.  Then  the  developed  form 
of  the  intersection  will  be  symmetrical  about  T  T.  Project  E  and 


H  over  to  Ei  and  Hi  for  the  top  and  bottom  of  the  curve.  Then 
to  find  intermediate  points  proceed  as  follows :  Draw  any  line 
K  L  parallel  to  P  Q  and  denoting  the  edge  of  a  plane  perpendicu- 
lar to  the  paper  and  cutting  both  cylinders.  On  F  G  as  diameter 
describe  the  circle  as  shown,  and  on  A  D  the  semi-circle  W  D  X. 
Make  N  0  equal  to  M  K  and  project  over  to  S,  thence  up  to  R 
and  then  over  to  T  T.  Rectify  the  arc  S  D  and  lay  off  Z  U  and 
Z  V  each  equal  to  the  rectified  length.  Then  will  U  and  V  be 


COMPUTATIONS  FOR  ENGINEERS. 


649 


points  on  the  curve  as  desired.  Other  points  may  be  found  in  a 
similar  manner  and  the  curve  filled  in. 

To  develop  the  form  of  the  smaller  cylinder  proceed  as  fol- 
lows : 

Let  Ci  Di  denote  in  the  development  the  element  H  G.  Lay 
off  Ai  Bi  =  the  circumference  I  F  J  G.  Then  for  the  points  cor- 
responding to  the  plane  K  L  take  d  Ei  =  G  Fi  =  the  developed 
length  of  the  arc  G  M.  Then  draw  Ei  Hi  and  F*.  h  each  equal 
to  K  R.  This  will  give  two  points,  Hi  and  /i,  and  others  may  be 
found  similarly  and  the  curve  filled  in  as  shown. 

[17]  To  Develop  the  Surface  of  a  Cone. 

Let  ABC  denote  the  cone.  With  A  C  as  radius  and  any 
point  0  as  center,  draw  an  arc,  G  H  K.  Then  lay  off  the  circum- 
ference of  the  base  A  B  (  —  3.1416  X  A  B)  on  a  strip  of  paper, 
and  lay  off  this  length  by  rolling  as  in  problem  [12]  from  G  to 
some  point  /.  Then  the  arc  G  H  I  =  circumference  of  A  B  and 
the  sector  0  G  H  J  is  the  developed  surface  of  the  cone. 

Gy 

L 


fi8]  To  Develop  the  Surface  of  the  Frustum  of  a  Cone. 

Referring  to  the  figure  for  the  preceding  problem,  let  A  D 
E  B  denote  the  frustum.  Then,  after  proceeding  as  in  that  prob- 
lem, take  next  a  radius  0  L  =  C  D  and  describe  the  arc  L  M  N. 
Then  will  the  sector  0  L  M  N  represent  the  surface  of  the  cone 
C  D  E,  while  the  strip  L  G  H  J  N  M  represents  that  of  the 
frustum. 

[19]  To  Develop  the  Segments  of  an  Elbow. 

These  are  portions  of  a  cylinder  cut  by  oblique  planes.  Let 
A  B  G  D  denote  such  a  segment.  Draw  L  M  perpendicular  to 
A  B  and  construct  the  semi-circle  L  Q  M.  L  M  may  be  placed  at 
any  convenient  location  between  B  C  and  A  D.  In  the  develop- 
ment let  E  F  denote  the  element  A  B.  Make  F  0  =  B  L  and 
then  draw  perpendicular  to  E  E  lines  TV  0  =  0  P  =  each  to  the 


650 


PRACTICAL  MARINE  ENGINEERING. 


semi-circumference  L  Q  M.  Then  N  P  is  the  development  of 
L  M.  Lay  offA/'G:=:P/  =  MCas  shown.  Then  to  find  inter- 
mediate points  on  G  F  I  take  any  line  R  S  and  project  down,  to 
T.  Develop  L  Q  T  and  lay  off  the  developed  length  at  0  U  and 
0  V.  Then  make  V  Y  and  U  W  each  equal  to  K  R,  and  F  and 


Y 

_____  —  —  -"" 

•~~-—>^^v 

V 

V 

0 

U 

Z 

'     ~-  _______ 

____^_  —  •—•     " 

< 

W  will  be  points  on  the  development  of  B  C.  Other  points  may 
be  found  in  a  similar  manner  and  the  development  of  B  C  com- 
pleted as  shown  by  the  curve  G  F  L  The  curve  H  E  J  as  the 
development  of  A  D  may  be  found  in  an  entirely  similar  man- 
ner, and  if  B  C  and  A  D  are  equally  inclined  to  the  elements  of 
the  cylinder,  L  M  will  naturally  be  located  midway  between  them, 
and  H  E  J  will  be  symmetrical  with  G  F  I  about  TV  P,  and  both 
may  thus  be  found  at  the  same  time  by  laying  off  above  and 
below  N  P  the  distances  determined  as  above  shown. 

Sec.  H.  PHYSICS. 
[i]  Acceleration  Due  to  Gravity. 

In  engineering  computations  there  frequently  enters  a 
quantity  known  as  the  acceleration  of  gravity  or  the  acceleration 
due  to  gravity,  and  denoted  by  the  symbol  g.  This  is  the  change 
per  second  which  the  gravity  or  attraction  of  the  earth  is  able  to 
bring  about  in  a  freely  falling  body.  For  engineering  purposes 
its  value  is  usually  taken  at  32.16  or  32.2. 

[2]  Specific  Gravity. 

The  specific  gravity  of  a  given  substance  is  the  relation  be- 
tween the  weights  of  equal  volumes  of  the  given  substance,  and 
of  some  standard  substance,  usually  water.  Thus  a  specific  grav- 


COMPUTATIONS  FOR  ENGINEERS. 


65' 


ity  of  8  means  that,  volume  for  volume,  the  given  substance  is  8 
times  as  heavy  as  water. 

[3]  Heat  Unit. 

Heat  is  measured  in  terms  of  a  unit  defined  as  the  amount  of 
heat  required1  to  raise  i  Ib.  of  water  I  deg.  in  temperature  at  62 
deg.  Fahrenheit,  or  from  62  deg.  to  63  deg. 

[4]  Specific  Heat. 

The  specific  heat  of  a  substance  is  the  relation  between  the 
amount  of  heat  required  to  raise  it  I  deg.  at  the  given  tempera- 
ture and  under  given  conditions  as  to  pressure  or  volume,  and 
the  unit  of  heat  as  just  defined.  Thus  a  specific  heat  of  .32  means 
that  under  the  given  conditions  it  will  require  to  raise  the  tem- 
perature i  deg.,  .32  of  the  heat  necessary  to  raise  i  Ib.  of  water 
from  62  deg.  to  63  deg. 

[5]  Expansion  of  Metals. 

Nearly  all  substances  expand  with  the  addition  of  heat,  and 
usually  with  nearly  equal  amounts  per  degree  rise  of  temperature, 
especially  where  the  substance  is  not  near  its  melting  or  boiling 
point.  The  following  table  gives  the  coefficient  of  linear  or  length 
expansion  for  various  substances.  This  is  the  expansion  in  unit 
length  for  i  deg.  Fahr.  rise  of  temperature. 


Substance. 

Coef. 

Substance. 

Coef. 

Aluminum 

000012^ 

Iron  cast 

Brass  cast  . 

0000006 

Iron   wrought 

Brass,  drawn  

.0000105 

Lead  

OOOOI  ^7 

Brick  

OOOOO^I 

Mercury 

Bronze    

OOOOO99 

Steel   cast 

.UOUU^j 

Bismuth  

OOOOOQ8 

Steel   wrought 

Concrete  

.  OOOOoSo 

Tin  .  .'  

00001  ]  6 

Conner  .  . 

OOOOO8Q 

Zinc 

0000141 

v_-yHFcl 

(jiass  

000004  s; 

To  find  the  expansion  in  the  length  of  any  bar  for  any  given 
rise  in  temperature  we  have  the  following: 

Rule — Multiply  the  coefficient  taken  from  the  table  by  the 
number  of  degrees,  and  this  by  the  length  of  the  bar,  and  the 
product  is  the  expansion  desired. 

Example:  What  is  the  expansion  of  a  steel  bar  20  ft.  long 
between  60  deg.  and  350  deg.  Fahr.? 

Ans.:    .0000069  X  290  X  20  =  .04  ft.  =  .48  in. 


6$2  PRACTICAL  MARINE  ENGINEERING. 

The  coefficient  for  area  or  surface  expansion  is  taken  twice 
that  for  linear  expansion,  and  that  for  cubic  or  volume  expansion 
is  taken  three  times  that  for  linear  expansion. 

Example:  What  is  the  increase  in  area  between  60  deg.  and 
300  deg.  Fahr.  in  a  copper  sheet  having  an  area  of  54  sq.  ft.? 

Ans.:    .0000178  X  240  X  54  =  -231  sq.  ft.  =  33.3  sq.  in. 

What  is  the  increase  in  volume  between  100  deg.  and  200 
deg.  Fahr.  in  a  piece  of  brass  having  a  volume  of  2  1-2  cu.  ft.? 

Ans.:    .0000288  X  100  X  2.5  =  .0072  cu.  ft.  =  12.44  cu.  in. 

Sec.  12.  MECHANICS. 

[l]  It  is  a  general  law  of  nature  that  all  bodies  tend  to 
remain  unchanged  as  regards  their  condition  of  rest  or  relative 
•motion.  A  body  at  rest  does  not  move  unless  caused  to  do  so 
by  some  outside  agency.  A  body  in  motion  continues  to  move 
until  it  is  brought  to  rest  by  outside  agencies  such  as  friction, 
resistance  of  the  air,  or  of  water,  etc. 

[«]  Force. 

Any  agency  which  changes  or  tends  to  change  the  condition 
of  a  body  as  regards  its  rest  or  relative  motion  is  called  a  force. 
For  engineering  purposes  force  is  measured  by  the  pound  or  ton 
as  unit.  In  marine  engineering  the  ton,  unless  otherwise  stated, 
is  usually  of  2,240  Ib. 

[3]  Specification  of  a  Force. 

A  force  has  three  characteristics  or  particulars  : 

(1)  Its  line  of  direction,  as  north  and  south. 

(2)  The  way  it  acts  in  that  line,  as  north. 
,    (3)  Its  magnitude. 

A  force  may  therefore  be  completely  represented  by  a  line 
A  B  of  length  to  represent  the  magnitude,  and  drawn  in  the 
direction  of  the  line  of  action  of  the  force. 


B 


Thus  the  force  A  B  would  mean  a  force  represented  in 
amount  according  to  some  scale  by  the  length  A  B,  and  acting 
along  the  line  A  B  from  A  to  B.  The  direction  of  action  is  also 
frequently  denoted  by  an  arrow  point,  thus  : 


B 


COMPUTATIONS  FOR  ENGINEERS.  653 

[4]  Moment  of  a  Force. 

This  is  the  product  of  the  magnitude  or  measure  of  the  force 
multiplied  by  the  perpendicular  distance  from  its  line  of  action 
to  a  given  reference  point. 

Thus  in  the  figure  let  the  full  line  represent  a  force,  P  denote 


its  measure,  and  0  the  reference  point.  Then  P  X  0  A  is  the 
moment  of  the  force  P  about  the  point  0.  In  the  term  moment 
of  a  force  a  point  of  reference  is  therefore  always  implied. 

[5]  Resultant. 

The  resultant  of  a1  system  of  forces  two  or  more  in  number 
with  their  lines  of  action  all  meeting  at  a  common  point,  is  the 
single  force  which  represents  the  combined  action  or  result  of  the 
system. 

[6]  Work. 

Work  is  done  when  a  force  (or  resistance,  as  it  may  be  called 
in  such  case)  is  overcome ;  as  for  example  when  a  weight  is  lifted 
or  a  ship  is  forced  through  the  water.  Work  is  measured  by  the 
product  of  the  resistance  by  the  distance  through  which  it  is 
overcome.  The  two  essential  factors  of  work  are  therefore 
force  or  resistance  on  the  one  hand,  and  motion  or  distance  on  the 
other.  The  unit  of  work  is  the  foot  pound  or  the  work  done  in 
raising  one  pound  weight  one  foot  in  height.  Thus  if  16  Ib.  be 
lifted  20  ft.  the  work  done  is  20  X  16  =  320  ft.  Ib. 

[7]  Power. 

Work  in  itself  is  independent  of  the  time  required  to  do  it, 
and  depends  simply  on  resistance  and  distance.  Power  means  a 
certain  amount  of  work  performed  in  a  given  time.  The  com- 
mon unit  is  the  horse  power,  which  is  33,000  ft.  Ib.  of  work  per- 
formed in  one  minute.  The  added  element  involved  in  power 
should  not  be!  forgotten.  Thus  33,000  ft.  Ib.  of  work  performed 
in  i  hour  would  not  mean  one  horse  power,  but  only  -fa  of  such 
amount,  while  33,000  ft.  Ib.  of  work  performed  in  I  second  would 
mean  60  horse  power.  Likewise  550  ft.  Ib.  per  second  represents 
one  horse  power  as  also  1,980,000  ft.  Ib.  per  hour.  To  find  the 
horse  power  in  any  given  case  we  have  therefore  the  following : 


654  PRACTICAL  MARINE  ENGINEERING. 

Rule  —  Find  the  foot  pounds  of  work  performed  per  minute 
and  divide  by  33,000. 

Example:  An  engine  in  one-half  hour  performs  118,800,000 
ft.  Ib.  work.  What  is  the  horse  power? 

118,800,000 

Horse  power  =  -  -  —  120 

3°  X  33>ooo, 

From  the  above  general  expressions  for  work  and  power 
there  come  two  forms  of  especial  interest  to  the  engineer.  These 
relate  to  the  work  done  by  or  on  a  fluid  in  a  cylinder  with  a 
moving  piston,  as  in  a  steam  engine  or  a  pump. 

Let  A  =  the  area  of  the  cylinder  in  square  inches. 

p  =  the  average  working  pressure  per  square  inch. 
L  =  the  length  of  stroke  in  feet. 

N  =  the  number  of  revolutions  or  double  strokes  per 
minute. 

Then  pA  =  the  average  total  pressure  or  load  on  the  piston. 
This  is  the  force  factor. 

2LN  =  the  distance  per  minute  assuming  the  engine  or 
pump  to  be  double  acting.  This  is  the  distance  factor. 

Then: 

Work  per  mt.  =  (pA)  X  &LN)  ft.  Ibs  ................  (a) 

or  as  it  is  frequently  written  by  changing  the  order  of  the  factors, 

Work  per  mt.  =  2pLAN  ft.  Ibs  .......................  (ai) 

To  reduct  this  to  horse  power  we  simply  divide  by  33,000 
and  have  : 

2pLAN 
Horse  power  = 


33,000 

Now  for  the  second  form  let  us  arrange  the  factors  thus  : 
Work  per  mt.  =  (p)  X  (2LNA). 

Then  multiply  p  by  144  and  divide  A  by  the  same  number. 
This  will  not  change  the  value  and  we  shall  have  : 

Work  per  mt.  =  (144  /)  x(-          -  J 

\     144     / 

The  first  factor  (i44/>)  is  the  pressure  per  square  foot.  Also 
A  -H  1  44  is  the  area  of  the  piston  in  square  feet  while  2LN  is  the 
distance  it  moves  through  per  mt.  measured  in  feet.  Hence 
2LN  A  -L-  1  44  is  the  volume  swept  through  per  mt.  Hence  we  have 
for  work  the  following  form  : 

Work  per  mt.  =  (pressure  per  unit  area)  X  (volume  swept 
through  per  mt.)  .  .  .  ..................  ...................  (b) 


COMPUTATIONS  FOR  ENGINEERS.  655 

In  this  form  it  must  be  noted  that  the  unit  area  and  the 
volume  must  both  refer  to  the  same  unit,  and  since  work  is 
measured  in  foot  Ibs.  this  unit  must  be  the  foot.  Hence  we  may 
write  more  definitely  : 

Work  per  mt.  =  (pressure  per  square  foot)  X  (volume 
swept  through  in  cubic  feet)  .............................  (bi) 

In  a  still  more  general  sense  when  a  liquid  is  moved  under 
pressure  we  may  put  volume  moved  or  change  of  volume  for  the 
second  factor  and  thus  write  : 

Work  per  mt.  =  (pressure  per  square  foot)  X  (volume 
moved  in  cubic  feet) 


[8]  Energy. 

This  is  the  capacity  for  performing  work,  and  depends  on 
special  conditions  of  motion  or  location.  For  convenience 
energy  is  considered  of  two  kinds. 

Kinetic  Energy  is  the  energy  possessed  by  a  body  in  virtue 
of  a  condition  of  motion.  As  we  know,  such  a  body  resists  an 
attempt  to  stop  it,  and  it  will  overcome  a  certain  resistance 
through  a  certain  distance  before  being  brought  finally  to  rest. 

W  v* 
This  kind  of  energy  is  measured  by  the  formula  E  =  --    where 

W  is  the  weight  in  pounds,  v  is  the  velocity  in  feet  per  second, 
and  g  is  the  acceleration  due  to  gravity  or  32.2.  Since  energy  is 
directly  convertible  into  work  it  must  be  really  similar  in  char- 
acter to  work,  and  we  may  therefore  speak  of  so  many  foot 
pounds  of  energy  just  as  well  as  of  so  many  foot  pounds  of  work. 
Potential  Energy  is  the  energy  possessed  by  a  body  in  virtue 
of  its  location  or  condition  relative  to  the  forces  acting  on  it. 
Thus  a  weight  lifted  to  the  top  of  a  building  has  potential  energy 
relative  to  the  street  because  it  could  do  \\  ork  if  allowed  to  move 
downward.  Similarly  a  compressed  spring  or  a  compressed  gas 
has  potential  energy  because  either,  if  properly  allowed  to  return 
to  the  condition  toward  which  it  tends,  will  perform  work.  Po- 
tential energy  is  measured  by  the  work  which  could  be  thus  per- 
formed, or  by  its  equal  the  work  which  must  be  done  upon  the 
body  in  order  to  produce  the  given  condition  ;  as  for  example  the 
work  done  in  lifting  the  weight  to  the  top  of  the  building,  or  in 
compressing  the  spring  or  gas.  Potential  energy  is  therefore 
measured  directly  in  foot  pounds. 


56  PRACTICAL  MARINE  ENGINEERING. 

[9]  Conservation  of  Energy. 

It  is  a  fact  of  universal  experience  that  energy  can  neither  be 
destroyed  nor  created.  The  seeming  appearance  or  disappear- 
ance of  energy  or  work  is  always  the  result  of  a  change  of  form. 
Energy  may  exist  in  a  variety  of  forms,  as  (i)  Mechanical,  (2) 
Thermal,  (3)  Electrical,  (4)  Chemical,  and  when  there  is  an  increase 
in  any  one  form  there  must  be  a  decrease  in  the  other  forms  of  exactly 
the  same  total  amount,  and  likewise  when  there  is  a  decrease  in  any 
one  form  there  must  be  an  increase  in  the  other  forms  also  of  exactly 
the  same  total  amount.  There  may  be  a  like  exchange  between 
kinetic  and  potential  energy,  the  one  increasing  as  the  other 
decreases,  and  vice  versa.  Thus  with  mechanical  energy  if  there 
is  no  change  to  other  forms  we  shall  find  that  the  sum  of  the 
kinetic  and  potential  energies  is  always  the  same,  and  that  one 
increases  as  the  other  decreases  and  vice  versa.  In  this  view  work 
simply  appears  as  an  attendant  upon  the  exchange  of  energy,  or 
more  definitely,  as  a  measure  of  the  exchange.  Again  if  we  fix 
our  attention  upon  one  body,  its  changes  of  total  energy  measure 
the  work  which  it  receives  or  gives  out.  If  its  energy  increases 
it  has  had  work  done  upon  it.  If  its  energy  decreases  it  has  given 
out  work  to  some  other  body. 

[10]  Statics. 

If  the  forces  which  act  on  a  body  are  properly  related  or 
balanced,  the  body  remains  at  rest.  The  conditions  necessary  to 
the  realization  of  this  state  of  rest  under  the  action  of  forces  form 
the  subject  of  statics. 

[11]  Dynamics. 

If  the  forces  are  not  so  related,  the  body  does  not  remain  at 
rest  and  motion  results.  The  amount  and  nature  of  such  motion 
and  its  relation  to  the  system  of  forces  form  the  subject  of 
dynamics. 

[12]  Propositions  in  Statics. 

Following  are  a  few  simple  propositions  in  statics  given 
without  proof: 

(1)  A  force  may  be  transferred  along  its  line  of  action  with- 
out changing  its  effect. 

(2)  Two  forces  equal  and  directly  opposite  will  balance  or 
produce  equilibrium. 

(3)  PARALLELOGRAM  OF  FORCES.    If  two  forces  whose  lines 
of  action  meet  in  a  point  0  are  represented  in  amount  and  direc- 


COMPUTATIONS  FOR  ENGINEERS. 


657 


tion  by  the  lines  0  A  and  0  B,  then  will  the  resultant  of  these 
two  forces  be  represented  also  in  amount  and  direction  by  the 
diagonal  0  C  of  the  parallelogram  0  A  C  B  erected  on  0  A  and 
0  B  as  adjacent  sides. 

(4)  A  force  0  G  represented  by  the  diagonal  0  C  reversed 
will  balance  0  C  or  the  resultant,  and  therefore  will  balance  P 
and  Q. 


c, 

(5)  POLYGON  OF  FORCES.  Let  there  be  a  system  of  forces 
represented  as  in  (a).  In  (b)  starting  at  any  point  Oi  and  Oi  Ai 
equal  and  parallel  to  0  A.  Then  from  A^  as  starting  point  draw 
Ai  Bi  equal  and  parallel  to  0  B,  and  so  on,  drawing  finally 
Ei  Fi  equal  and  parallel  to  0  F.  Then  will  the  closing  line  Oi  Fi  in 
direction  and  amount  represent  the  resultant  of  the  system  of 
forces,  while  (X  Fi  reversed,  or  Fi  Oi  will  represent  similarly  the 
balancing  force  of  the  system — that  is,  the  single  force  which 
will  balance  the  system  and  with  it  produce  equilibrium.  In  the 


construction  in  (b)  the  order  in  which  the  forces  are  taken  is  in- 
different, but  we  have  here  supposed  them  taken  in  regular  order 
to  the  right,  beginning  with  0  A  and  ending  with  0  F. 

It  is  readily  seen  that  this  proposition  is  a  generalization  of 
(3)  extended  to  cover  the  case  of  any  system  of  forces.  It  follows 
from  this  proposition  that  if  any  system  of  forces  may  be  repre- 
sented as  in  (b)  by  the  sides  of  a  completely  closed  polygon,  then 
such  system  will  produce  equilibrium,  for  the  resultant  in  such  case 
would  be  zero.  Again  in  such  case  any  force  may  be  considered 
as  the  balancing  force  for  the  system  composed  of  all  the  others, 


658 


PRACTICAL  MARINE  ENGINEERING. 


and  any  force  reversed  may  be  considered  as  the  resultant  of  the 
system  composed  of  all  the  others. 

(6)  COMPONENTS.  In  the  figure  the  two  forces  P  and  Q 
are  at  right  angles.  In  such  case  they  are  known  as  the  com- 
ponents, or,  more  correctly,  the  rectangular  components,  of  their 
resultant  R  along  the  lines  0  D  and  0  E.  In  general  the  com- 
ponent 0  B  of  any  force  0  C  along  any  line  0  E  is  found  by  draw- 
ing from  C  a  line  C  B  perpendicular  to  0  E,  thus  determining  the 
length  0  B. 

D 


0 


B    E 


(7)  CONDITIONS  FOR  EQUILIBRIUM.    The  conditions  for  the 
equilibrium  of  any  body  are  as  follows  : 

(a)  The  sum  of  all  the  components  of  all  the  forces  acting 
on  the  body  taken  along  any  line,  or  more  particularly  along  any 
pair  of  lines  at  right  angles,  must  balance. 

(b)  Taking  any  point  as  origin,  the  sum  of  the  moments  of 
all  the  forces  tending  to  turn  the  body  in  one  direction  about  this 
origin  must  equal  or  balance  the  corresponding  sum  in  the  other 
direction. 

If  all  the  forces  act  through  a  single  point,  only  the  first  of 
these  conditions  is  necessary.  If  instead  they  act  through  dif- 
ferent points  of  a  body,  both  conditions  are  necessary. 

(8)  PARALLEL  FORCES.    The  resultant  of  a  system  of  parallel 
forces  is  the  algebraic  sum  of  the  forces. 

The  center  of  a  system  of  parallel  forces  is  a  point  such  that 
if  a  force  equal  and  opposite  to  the  resultant  be  here  applied,  the 
whole  system  will  be  maintained  in  equilibrium. 

Or  otherwise,  it  is  che  point  at  which  the  resultant  of  the 
whole  system  may  be  considered  as  acting. 

The  center  of  gravity  of  a  body  is  the  center  of  the  system  of 
sensibly  parallel  forces  due  to  the  attraction  of  gravitation. 

Or  otherwise,  it  is  the  point  at  which  the  entire  weight  of  the 
body  may  be  considered  as  centered,  or  through  which  it  may 
be  considered  as  acting. 


COMPUTATIONS  FOR  ENGINEERS.  659 

Or  otherwise,  it  is  the  point  of  the  body  which,  if  supported, 
the  whole  body  will  be  supported  in  equilibrium,  and  perfectly 
free  to  turn  into  any  position. 

[13]  Mechanical  Powers. 

LEVER.  A  lever  consists  essentially  of  a  bar  which  supports 
a  weight  or  applies  a  force  at  one  point  by  means  of  a  force  ap- 
plied at  another  point,  the  bar  in  the  meantime  being  supported 
and  turning  about  a  third  point  called  the  fulcrum.  According 
to  the  relation  of  these  three  points,  levers  are  divided  into  three 
classes  as  below : 

LEVER  OF  THE  FIRST  CLASS.     In  this  the  fulcrum  R  is  be- 

M- I ~ 

U- a -M*-  b  -»n 


R* 
P 

tween  the  points  of  application  of  the  forces  P  and  W '.    The  fol- 
lowing proportions  and  equations  apply  to  this  case : 
P  \W  ::b  :aorPa=Wb 

p  :    P+W  ::b  :  I  or  P  l=(P+W)b 
W  :    P  +  W  : :  a  :  I  or  W  I  =  (P  +  W)  a 


/>  +  v\ 
p 


-  b  I  v  -  W       ~  P  +  n 

LEVER  OF  THE  SECOND  CLASS.    In  this  the  weight  lifted  or 
resultant  force  W  is  between  the  applied  force  P  and  the  fulcrum 


a *t*-  b  -M 


W 


R.    The  following  proportions  and  equations  apply  in  this  case : 
P  :    W  : :  b  :  /  or    P  1  =    W  b 

—  P)  b 


66o  PRACTICAL  MARINE  ENGINEERING. 

LEVER  OF  THE  THIRD  CLASS.  In  this  the  applied  force  P 
is  between  the  weight  lifted  or  resultant  force  W  and  the  fulcrum 
R.  The  following  proportions  and  equations  apply  to  this  case : 

P  \W  : :  /  :  a    or    P  a—W  I 
(p—W):W::b:a    or    (P  —  W}  a  =  W  b 
(P—W):P::b:l    or    (P  —  W)  I  =  P  b 
II  W  W 

P  =  L  w  =  ~(P-  m 

a  b  v 


An  ordinary  crowbar,  a  pair  of  scissors,  an  air  pump  lever,  are 
all  examples  of  a  lever  of  the  first  class.  A  pair  of  nut  crackers, 
an  oar  (the  water  being  the  fulcrum),  and  often  many  of  the 
levers  about  the  starting  and  drain  gear  of  an  engine,  are  ex- 
amples of  a  lever  of  the  second  class.  The  forearm  (the  elbow 
being  the  fulcrum),  or  a  ladder  when  raised  against  a  house,  are 
examples  of  the  third  class. 

WINDLASS  AND  CRANK.  In  this  device  a  barrel  B  is  carried 
on  an  axle  supported  in  bearings  at  A  and  C,  and  operated  by  a 
crank  D.  The  weight  W  may  then,  by  means  of  a  rope  wound 
on  the  barrel,  be  raised  or  lowered  by  the  action  of  a  force  P 


applied  at  the  crank.    The  following  proportions  and  equations 
give  the  relations  between  the  various  quantities  concerned  : 

P:    W  ::  r  :  R  or  P  R  =  Wr 
P      =      ~  W   W=^P 
P  W 

WR  R-^pr 

r   =  radius  of  barrel. 
R  =  radius  of  crank. 


COMPUTATIONS  FOR  ENGINEERS. 


WHEEL  AND  AXLE.  This  device  is  the  same  as  the  pre- 
ceding, except  that  the  wheel  A  takes  the  place  of  the  crank. 
The  same  proportions  and  equations  apply  as  for  the  windlass 
and  crank  above.  Illustrations  of  the  principles  involved  in  this- 
and  the  preceding  figures  are  found  in  all  forms  of  windlasses, 
deck  winches,  etc. 

r   =  radius  of  barrel. 
R  •=.  radius  of  wheel. 


**, 


I 


w 


GEARED  HOIST.  This  device  is  similar  to  the  two  preced- 
ing, with  the  addition  of  gearing  between  the  force  P  and  the 
weight  W.  The  following  equations  apply  to  this  case : 


P 

W 

P  , 


,  r, 


w 


Most  deck  winches  are  illustrations  of  a  simple  geared  hoist. 

7?i  =  radius  of  A 

n  :=   radius  of  B 

R2  =  radius  of  C 

rz  —  radius  of  D 

SINGLE  FIXED  PULLEY.  A  is  a  pulley  or  sheave  supported 
from  R  and  turning  about  its  center.  B  C  is  a  single  rope  led 
over  the  pulley,  to  one  end  of  which  the  force  P  is  applied,  and 
to  the  other  end  of  which  the  weight  W  is  attached.  The  follow- 
ing equations  apply  to  this  case : 


662 


PRACTICAL  MARINE  ENGINEERING. 


P  =  W 

R  =  P  +  W  =  2P 
Velocity  of  W  =  velocity  of  P 

A  single  whip  used  for  raising  light  weights  is  an  illustration  of 
this  purchase. 


SINGLE  MOVABLE  PULLEY.  A  is  a  pulley  or  sheave  to  the 
frame  of  which  is  attached  the  weight  W.  B  C  is  the  rope  rove 
around  the  sheave,  having  one  end  made  fast  to  the  support  D, 
while  to  the  other  is  applied  the  force  P.  The  following  equa- 
tions apply  to  this  case  : 

W  =    2   P 

W 
R  =  P  =  — 

2 

Velocity  of  W  —  1-2  velocity  of  P 

Tacks  and  sheets  on  light  sails  are  illustrations  of  this  form  of 
purchase. 

tfl 


B 


W 


LUFF  TACKLE.    In  this  purchase  there  are  two  sheaves  at  A 
and  one  at  B.    The  rope  is  led  as  shown  from  the  frame  of  B  up 


COMPUTATIONS  FOR  ENGINEERS. 


663 


around  one  of  the  sheaves  A,  then  down  around  the  sheave  B  and 
up  over  the  other  sheave  A  to  the  point  P,  where  the  power  is 
applied.  The  following  equations  apply  to  this  case : 

W  =  3P 
R  =     4  P 
If  upper  block  is  fixed, 

Velocity  of  W  =  1-3  velocity  of  P. 
If  lower  block  is  fixed, 

Velocity  of  R  =  1-4  velocity  of  P. 

In  order  to  obtain  the  greatest  advantage  with  this  purchase, 
therefore,  B  should  be  the  fixed  block. 

A  PAIR  OF  BLOCKS,  AS  IN  THE  LUFF  TACKLE  FIGURE,  WITH 
ANY  NUMBER  OF  SHEAVES  IN  EITHER  BLOCK. 
W       total  number  of  ropes  at  the  lower  block,  passing  through 
P    ~  and  attached. 

R  total  number  of  ropes  at  the  upper  block,  passing  through 
P  ~  and  attached. 

Thus  in  the  figure  the  number  of  ropes  at  the  lower  block  is  3 
and  the  number  at  the  upper  block  is  4,  which,  according  to  the 
rule,  would  give  the  same  relations  between  P,  R  and  W  as  in 
the  equations  above. 

R 


W 


DIFFERENTIAL  PULLEY.  In  this  purchase  there  are  two 
sheaves  at  A  fastened  together,  or  made  in  one  piece,  and  one 
sheave  at  B.  A  rope  or  chain  is  rove  as  shown  in  the  figure,  and 


664 


PRACTICAL  MARINE  ENGINEERING. 


the  force  is  applied  at  P  while  the  weight  W  is  supported  from 
the  lower  block.    The  following  equations  apply  to  this  case  : 

R  =  radius  of  larger  upper  pulley 
r  =  radius  of  smaller  upper  pulley 

W          2  R 
Then     -p-=^-_- 


- 


Velocity  of     W  = 


(velocity  oLP) 


The  differential  pulley  is  commonly  found  in  all  engineer's  out- 
fits on  board  ship. 

P 


INCLINED  PLANE. 


W       & 
P   ~  h 


W     :    :  P 


and  P  =    -.    W 

o 


WEDGE. 


R 


R   =    'IP 
a 


and     P  =    T 


COMPUTATIONS  FOR  ENGINEERS.  665 

SCREW. 

p    =  pitch  of  screw 
P  =  force  applied  at  radius  r 
W  =  pressure  exerted 
P  :  W  ::p  :     2  TT  r 

or  P  :  W  : :  p  :  6.2832  r 

^ 

6.2832  r  „ 
or  W    =  -  -  P 

P 

P  P      -  W 

'-    6.2832  r  V 


Examples  of  the  applications  of  the  last  three  figures  will  be  too 
familiar  to  need  special  mention. 

[14]  Examples  in  Mechanics. 

We  give  below  the  solutions  of  a  few  simple  examples  as  il- 
lustrations of  the  preceding  principles  of  mechanics.  In  all  cases 
the  effects  of  friction  are  omitted. 

(1)  In  a  lever  of  the  first  class  as  shown,  a  =  48  and  6  =  8. 
With  a  pull  P  of  1 60  lb.,;  what  weight  W  can  be  raised? 

W   :=  a.P=  ^   X    160  „  960  Ib. 

O  o 

(2)  In  a  lever  of  the  second  class  as  shown,  /  =  72  "  and 
b  =  12 " '.    What  force  P  will  be  required  to  raise  a  weight  W 
of  600  Ib.? 

P  =  ~   W  =~    X    600  =:    ioo  Ib. 
/  72 


666  PRACTICAL  MARINE  ENGINEERING. 

(3)  In  a  lever  of  the  third  class  as  shown,  /  =  40  "  and  W 
—  30  Ib.  Where  must  a  force  P  of  80  Ib.  be  located  so  as  to 
maintain  equilibrium? 


(4)  The  dimensions  of  a  windlass  and  crank  as  illustrated 
are  as  follows:  Radius  of  crank  =  14".     Radius  of  barrel  = 
41-2  ".    What  weight  can  be  raised  with  a  force  of  60  Ib.  applied 
at  the  crank? 

W  =  —  P  =  -,    X    60   =  186   2-3  Ib. 

r  44 

(5)  With  a  wheel  and  axle  as  illustrated,  the  diameter  of  the 
wheel  is  6'  and  of  the  axle  10  ".    What  force  P  will  be  required 
to  hoist  a  weight  W  of  600  Ib.? 

p  =  Z   W  =  4r  X    6o°  =  83   i-3  lb- 
K  36 

(6)  The  dimensions  of  a  geared  hoist  as  illustrated  are  as 
follows  :    Diam.  of  A  =  24  "  ;  number  of  teeth  in  B  —  16  ;  num- 
ber of  teeth,  in  C  =  96;  diam.  of  D  =  10".     What  weight  W 
can  be  hoisted  if  P  =  100  lb.? 

Since  the  diameters  and  radii  of  wheels  are  in  the  same  ratio 
as  their  numbers  of  teeth,  we  have  : 

*'  8  X  *8  X   I0°   =:    I44o  lb. 


r*ra  8x5 

(7)  With  a  single  movable  pulley  as  illustrated,  what  weight 
can  be  raised  with  a  pull  P  of  90  lb.? 

W  =  2  P  =  2  X  90  =  180 

(8)  With  a  luff  tackle  purchase  as  illustrated,  what  force  P 
will  be  required  to  raise  a  weight  W  of  372  lb.,  and  what  will  be 
the  load  at  R? 

W  =  3  P  or  P  =  W  -f-  3  =  372  +  3  =  124 
R  =  4  P  =  4  X  124  =  496 

(9)  The  dimensions  of  a  differential  pulley  as  illustrated  are 
as  follows  :    Larger  diameter,  13  "  ;  smaller  diameter,  n  ".    With 
a  pull  P  of  80  lb.,  what  weight  W  can  be  raised? 

T/r7  2  R  2  x  6J  x  80 

W  =   -£—    -  P  =   -  -   -   1040  ID. 

R-r  6J  -  5J 


COMPUTATIONS  FOR  ENGINEERS. 


667 


(10)  An  inclined  plane  as  illustrated  has  dimensions  as  fol- 
lows :  Slant  length,  b  =  72  " ;  height,  h  ==  18  ".  With  a  pull  P 
of  40  lb.,  what  weight  W  can  be  moved  up  the  plane? 

W  =  %  P  =   7~s   X    40  ==    1 60  lb. 

(n)  A  wedge  as  illustrated  has  the  following  dimensions: 
Back,  a  =  4  " ;  length,  h  •=  26  " .  What  resistance  R  can  be  over- 
come by  a  force  P  of  216  lb.? 

Ji    7,        26 

R  —  -  P  =  -  -  x  216  =   1404  lb. 
a  4 

(12)  A  screw  as  illustrated  has  the  following  dimensions : 
Pitch  p  =  1-4  " ;  radius  r  =  12  " ;  force  P  =  60  lb.  What  pres- 
sure W  can  be  exerted? 

6.2832  x   12  X  60 


(13)  Given  a  boiler  brace  0  A  with  crowfoot  or  forked  at- 
tachment to  the  plate  B  C.  With  a  known  load  on  0  A,  required 
the  load  on  0  B  and  0  C. 

Evidently  the  three  forces  on  0  A,  0  B  and  0  C  keep  the 
joint  0  in  equilibrium.  If  represented  according  to  the  polygon 
of  forces  [12]  (5),  they  must  form  a  closed  triangle.  This  is  rep- 
resented by  0  A  D,  where  0  A  represents  the  force  on  the  brace, 
A  D  that  on  0  B  and  D  0  that  on  0  C.  Hence  if  0  A  is  laid 
down  to  some  convenient  scale  to  represent  the  load  on  the 
brace,  then  A  D  and  D  0  respectively  will,  according  to  the 
same  scale,  represent  the  loads  on  O  B  and  0  C. 


(14)  Given  a  boiler  brace  0  A  oblique  to  the  shell  C  D. 
With  a  known  load  in  the  direction  B  0,  required  the  load 
on  0  A. 


668 


PRACTICAL  MARINE  ENGINEERING. 


The  point  of  attachment  0  is  again  maintained  in  equilib- 
rium by  the  action  of  the  three  forces,  one  along  0  A,  one  in 
the  direction  B  0,  and  a  third  C  existing  as  a  tension  in  the 
plate.  The  triangle  of  forces  in  this  case  is  represented  by  0  B  A. 
Hence  if  0  B  is  laid  off  to  any  scale  to  represent  the  known  load, 
then  will  0  A  represent  to  the  same  scale  the  resulting  load  on 
the  brace. 

(15)  Let  C  A  B  0  represent  the  moving  parts  of  an  engine. 
With  a  known  piston  load  acting  along  C  A,  required  the  re- 
sultant loads  on  the  connecting  rod  and  on  the  guide. 

The  point  A  is  kept  in  equilibrium  by  the  action  of  the  three 
forces,  one  acting  down  along  C  A,  one  acting  up  the  rod  along 
B  A  and  one  acting  from  the  guide  along  DA.  It  is  the  two 
latter  which  are  required.  The  triangle  of  forces  in  this  case  is 


represented  by  A  E  F.  Hence  if  A  E  is  laid  off  to  represent  to 
any  convenient  scale  the  known  piston  load,  then  to  the  same 
scale  will  A  F  and  £  F  represent  the  loads  on  the  connecting 
rod  and  crosshead  respectively.  It  thus  appears  that  the  load 
on  the  connecting  rod  is  in  general  greater  than  that  on  the 
piston  rod,  and  that  it  is  greater  in  the  same  ratio  that  any  length 
A  F  is  greater  than  the  corresponding  distance  A  E. 

(16)  Let  the  diagram  represent  a  davit  C  D  supporting  a 
weight  W  and  braced  by  a  stay  A  B.  With  a  given  weight  W, 
required  the  tension  on  the  stay  and  the  forces  at  the  foot  of 
the  davit. 

The  tension  T  may  be  represented  by  its  two  components 
P  and  Q,  and  the  reaction  at  C  by  two  components  N  and  R.  In 


COMPUTATIONS  FOR  ENGINEERS. 


669 


this  case  we  require  the  use  of  both  conditions  of  equilibrium, 
and  without  giving  all  details  we  will  simply  write  the  equations 
and  the  resulting  values  of  the  forces. 

Equating  vertical  forces          W  +   Q  =  N 
Equating  horizontal  forces  P  =  R 


Taking  moments  about  C 
We  also  have 


W  a  =  Ph 


r>- 

From  these  equations  we  find  : 


Q  = 


W 


=    *4     w 


R  = 


N 


I 

a  -f 


(a  -f-  ^\ 
=  \~~F~) 


w 


W 


670  PRACTICAL  MARINE  ENGINEERING. 


Answers  to  Examples  in  Part  II. 


Sec.  i.  COMMON  FRACTIONS. 

i>]  -v7-,  v-,  w,  vy,  w  w.  -fit-- 

[3]    5ii  'i  2TvT,  2|,  4,  if,  3*.  4oTV 

[4]     *,  fV>   «A.  i  W,  T¥T,   iA.   3,  t- 

[6]    i^»  4.  4,  2fV  isff.  27^  H»  4Ht,  AY,  A* 

[7]     4,   2,    2T2T,   3-i-,   9|,   7,    2j. 

[8]       T3^     A,     TV,     A.     T3>     i     A- 

[9]     f  A.  W.  A.  if'   'I.  9t,  it.  «.   i*.  iff'  TV 

[10]       T5¥,     I  Of,     f- 

Sec.  2.  DECIMAI,  FRACTIONS. 

[5]  .4,  2.4,  24.4,  .072,  .1307+,  4.5,  2.6,  1.1951+,  .001875, 

.007368+,  3.2857  +  . 

[8]  3.808,  3466.892,  .21888,  93978.89.  .0294,  .000504. 
[9]  .4531+,  11.334+,  0000006.,  600,  4000,  500. 


MISCELLANEOUS  EXERCISES.  671 


MISCELLANEOUS    EXERCISES. 

(1)  One  ton  of  coal  is  found  to  contain   300  pounds  of 
ashes.  What  percent  is  combustible  and  what  percent  ashes? 
(See  Part  II,  Sec.  3). 

Ans.  86.6%  and  13.4%. 

(2)  In  a  certain   boiler  it  requires  1,120  heat  units  to  evap- 
orate one  pound  of  water.    With  the  addition  of  a  feed  heater 
this  is  reduced  to  1,030.     Find  the  percent  of  saving.  (See  Part 
II,  Sec.  3). 

Ans.  8.04%. 

(3)  A  ship  steams  2,800  miles  in  11  days.     How  long  will 
it  require  to  steam  740  miles  at  the  same  rate?     (See  Part  II, 
Sec.  6), 

Ans.  2.9  days. 

(4)  A  given  engine  with  a  reduced  mean  effective  of  36 
pounds,  stroke  33  inches  and  revolutions  of  120  develops  1,200 
I.  H.  P.    With  revolutions  140  and  stroke  30  inches  what  would 
be  the  reduced  mean  effective  for  1,300  I.  H.  P.     (See  Part  II, 
Sec.  6  [2]). 

Ans.  36.77. 

(5)  A  propeller  at  90  revolutions  and  24  per  cent  slip  gives 
a  speed  of  12  miles  per  hour.    With  TOO  revolutions  and  26  per 
cent  slip  what  speed  will  be  attained?     (See  Part  I,  Sec.  80; 
Part  II,  Sec.  6). 

Ans.  12.98. 

(6)  How  many  gallons  of  oil  will  be  contained  in  a  tank  of 
rectangular  form,  4  feet  long,  27  inches  wide  and  2  feet  high? 
(See  Part  II,  Sec.  4  [5l,  Sec.  9  [16]). 

Ans.  134.6. 


672  PRACTICAL  MARINE  ENGINEERING. 

(7)  An  oil  tank  55  inches  long  has  trapezoidal  cross  sec- 
tions.    The  two  parallel  sides  are  28  inches  and  40  inches,  and 
the  distance  between  them  is  40  inches.     Find  the  capacity  in 
gallons.    (See  Part  II,  Sec.  4  [5],  Sec.  9  [4]  [16]). 

Ans.  323.8. 

(8)  What  is  the  capacity  of  a  pump  in  gallons  per  mt.  if 
the  cylinder  is  9  inches  in  diameter,   10  inches  stroke  and  60 
strokes  per  mt.?    (See  Part  II,  Sec.  4  [5],  Sec.  9  [17]). 

Ans.  165.2. 

(9)  A  coal  bunker  of  rectangular  form  is  18  feet  fore  and 
aft,  40  feet  wide  by  13  feet  deep.     Find  the  capacity  in  tons,  al- 
lowing 42  cu.  ft.  per  ton.    (See  Part  I,  Sec.  n  [7]  ;  Part  II,  Sec. 
9  [16]). 

Ans.  223. 

(10)  A  coal  bunker  of  irregular  form  has  three  cross  sec- 
tions, as  follows :  The  first  is  a  rectangle  12  ft.  by  18  ft.    The  sec- 
ond is  a  trapezoid  with  parallel  sides  12  and  10  ft.  by  16  ft.  be- 
tween them,  and  the  third  is  a  trapezoid  with  parallel  sides  12 
and  8  ft.  by  14  ft.  between  them.   .  These  sections  are  24  feet 
apart.    Find  the  capacity  in  tons  of  44  cu.  ft.  each. 

Solution.  The  areas  of  the  three  sections  are  as  follows : 
216,  176,  140.  Then  by  Simpson's  rule,  Part  II,  Sec.  9  [15] 
[29]  the  volume  is  bound  as  follows :  V  =  (216  +  4  X  176  + 
140)  -T-  3  X  24,  or  Volume  =  8,480  cu  ft. 

Then  tons  =  8,480  -f-  44  =  192.7. 

(n)  An  oil  can  in  the  form  of  a  frustum  of  a  cone  is  n 
inches  high,  and  the  diameters  of  the  base  and  top  are  respect- 
ively 5  and  4  inches.  Find  the  capacity.  (See  Part  II,  Sec.  9 

[26]). 

Ans.  .76  gallon. 

(12)  Will  a  boiler  60  in.  diam.,  y2  in.  thickness  of  plate 
stand  as  much  pressure  as  a  boiler  48  in.  diam.,  T7¥  in.  thickness 
of  plate?    (See  Part  I,  Sees.  19,  63). 

Ans.  No. 

(13)  Find  the  required  weight  for  a  safety  valve  whose 
diam.  is  4",  fulcrum  3",  length  of  lever  34",  weight  of  lever  \? 
Ibs.,  weight  of  valve  and  stem  6  Ibs.,  steam  pressure  65  Ibs.    (See 
Part  I,  Sec.  61). 

Ans.  65.5  pounds. 

(14)  What  would  be  the  safe  working  pressure  of  a  boiler 


MISCELLANEOUS  EXERCISES.  673 

i. 08  in.  thickness  of  plate,  tensile  strength  60,000  Ibs.  per  sq.  in. 
diameter  of  boiler  12  ft.?    (See  Part  I,  Sec.  19). 

Ans.   150  pounds  per  square  inch  for  single  riveting  or  180 
pounds  per  square  inch  for  double  riveting. 

(15)  The  diameter  of  a  boiler  shell  is  15  feet.    The  work- 
ing  pressure    desired    is    180   pounds    per    square    inch.      The 
strength  of  the  material  is  60,000  pounds  per  square  inch.    Find 
the  thickness  with  double  riveting.     (See  Part  I,  Sec.  19). 

Ans.   1.35  inches  or    say  i%. 

(16)  The  diameter  of  a  steel  screw  stay  bolt  at  bottom  of 
thread  is  il/4  inches.    The  area  supported  by  each  is  49  square 
inches.    Find  the  pressure  allowed.    (See  Part  1,  Sec.  19). 

Ans.  200  pounds  per  square  inch. 

(17)  What  would  be  the  thickness  of  plate  required  for  the 
same  boiler  as  in  (16)  the  spacing  being  7  by  7  inches,  and  the 
bolts  being  simply  riveted  over  on  ends?    (See  Part  I,  Sec.  19). 

Ans.  17-32  in. 

(18)  For  other  problems  in  boiler  bracing  see  Part  I,  Sec. 
62. 

(19)  Temperature  of  feed  160°.  Steam  pressure  180  pounds 
gauge.     Quality  of  steam  97  per  cent.     Thermal  value  of  coal 
13,800  thermal  units  per  pound.     Efficiency  of  boiler  .68.     Find 
the  pounds  of  water  evaporated  per  pound  of  coal  into  steam  of 
the  given  quality.    (See  Part  I,  Sec.  58). 

Ans.  8.76  pounds. 

(20)  With  a  coal  consumption  of   1.80  per  I.  H.   P.  per 
hour  how  much  coal  will  be  required  in  the  bunkers  of  a  ship 
making  a  lo-day  trip,  the  I.  H.  P<  being  1,800  and  a  margin  of 
12%  being  allowed  for  emergencies?    (See  Part  I,  Sec.  59). 

Ans.  388.8  tons. 

(21)  A  corrugated  furnace  has  a  diameter  of  44  inches  and 
thickness  of  1-2  inch.     Find  the  pressure  allowed.  (See  Part  I, 
Sec.  19). 

Ans.   170  or  159,  according  to  the  style  of  corrugation. 

(22)  Find  the  necessary  thickness  of  a  copper  steam,  pipe 
for  200  pounds  working  pressure,  the  diameter  of  the  pipe  being 
9  inches.    (See  Part  I,  Sec.  19). 

Ans.  .2875  inch. 

(23)  With  cut  off  at  62  per  cent  of  stroke  and  clearance  of 
12  per  cent,  what  is  the  expansion  ratio?   (See  Part  I,  Sec.  68). 

Ans.   1.51. 


674  PRACTICAL  MARINE  ENGINEERING. 

(24)  The  I.  H.  P.  is  2,100,  pitch  of  propeller  18  feet,  revo- 
lutions 100.    Find  the  indicated  thrust  in  pounds.      (See  Part  I, 
Sec.  71). 

Ans.  38,500  pounds. 

(25)  What  is  the  weight  of  a  rectangular  piece  of  boiler 
plate  14  feet  long,  5  feet  6  inches  wide  and  I  1-8  inch  thick?  (See 
table  page  30). 

Ans.  12,474  cu.  in.  -  -  3,530  pounds. 

(26)  Given  speed  of  ship   12  knots,  revolutions   no,  slip 
of  propeller  20  per  cent,  find  the  pitch.    (See  Part  I,  Sec.  80  [i]). 

Ans.  13.8  ft. 

(27)  Allowing  an  Admiralty  constant  of  280,  what  would 
be  the  I.  H.  P.  required  for  a  displacement  of  8,600  tons  with  a 
speed  of  10  knots?    (See  Part  I,  Sec.  82). 

Ans.  1,500. 

(28)  Given  speed  of  ship  18  knots,  revolutions  no,  pitch  20 
feet.    Find  the  slip  ratio.    (See  Part  I.,  Sec.  80  [i]). 

Ans.  17.1  per  cent. 

(29)  Given  the  pitch  of  a  propeller  54  inches,  revolutions 
360,  slip  21  per  cent.     Find  the  speed  in  miles  per  hour.     (See 
Part  I.,  Sec.  80  [i]). 

Ans.  14.54. 

(30)  Given  the  diameter  of  the  rolling  circle  of  a  paddle 
wheel  30  feet,  slip  28  per  cent.,  revolutions  24.     Find  the  speed 
in  miles  per  hour. 

Ans.  18.5. 

(31)  Given  displacement  120  tons,  I.H.P.  420.   Allowing  an 
Admiralty-Constant    of    160,    what    speed    may    be    expected? 

(See  Part  L,  Sec.  82). 
Ans.  14.03  knots. 

(32)  Given  I.H.P.  =  33,ooo,  D  =  20,000,  speed  =  23  knots. 
Find  the  Admiralty-Constant.    (See  Part  L,  Sec.  82). 

Ans.  272. 

(33)  Allowing  an  Admiralty-Constant  of  no,  what  would  be 
the  I.H.P.  required  for  a  displacement  of  4  tons  at  a  speed  of  7 
knots*11    (See  Part  L,  Sec.  82). 

Ans.  7.86. 

(34)  On  a  trial  trip  over  a  course  of  two  nautical  miles, 
suppose  the  observations  as  follows  : 

Run  North  2  m.  36  sec.    Revolutions  648. 
Run  South  2  m.  24  sec.    Revolutions  604. 


MISCELLANEOUS   EXERCISES.  675 

Pitch  of  propeller  24  feet.     Find  average  speed  and  slip  of 
propeller.    (See  Part  L,  Sec.  84). 
Ans.  24  knots,  19  per  cent. 

(35)  Given  the  ship  in  example  (27).     With  the  same  Ad- 
miralty-Constant, what  percentage  increase  in  power  would  be 
required  for  30  per  cent,  increase  in  displacement?    (See  Part  L, 
Sec.  82). 

Ans.  19  per  cent. 

(36)  Given  the  ship  in  example  (27).     With  an  Admiralty- 
Constant  of  250,  what  percentage  increase  in  power  would  be 
required  for  a  30  per  cent,  increase  in  speed?     (See  Part  I., 
Sec.  82). 

Ans.  146  per  cent. 


676 


PROPERTIES  OF  SATURATED  STEAM* 


Vacuum  Gauge, 
Inches  of  Mer- 
cury, 

Absolute  Press- 
ure. Ibs.  per 
square  inch. 

yS 

*% 

11 
f 

Total  Heat 
above  32  -  F. 

Latent  Heat  L. 

=  II-  h. 
Heat-  units. 

Relative  Volume. 
Vol.  of  Water 
at  39  F.  =  i. 

Volume  Cn.  ft. 
in  1  Ib.  of  bteam. 

Weight  of  1  cu 
ft.  {-team  Ib. 

In  the 
Water 
h 
Heat- 
units. 

In  the 
Steam 
H 
Heat- 
units. 

29.74 

.089 

32 

0 

1091.7 

1091.7 

208  80 

3333.3 

.00030 

29.67 

.122 

40 

8 

1094.1 

1086.1 

154330 

2472.2 

.00040 

29.56 

.176 

50 

18 

1097.2 

1079.2 

107630 

1724.1 

.00053 

29.40 

.254 

60 

28.01 

1100.2 

1072.2 

76370 

1223.4 

.00082 

29.19 

.359 

70 

38.02 

1103.3 

1065  3 

54660 

875.61 

.00115 

28.90 

.502 

80 

48.04 

1106.3 

1058.3 

39690 

635.80 

.00158 

28.51 

.692 

90 

58.06 

1109.4 

1051.3 

29290 

469.2) 

.00213 

28.00 

.943 

100 

68.08 

1112.4 

1044.4 

21830 

349,70 

,00286 

27.88 

1 

102.1 

7009 

1113.1 

1043.0 

20623 

334.23 

.00299 

25.85 

2 

126.3 

94.44 

1120.5 

1026  0 

10730 

173,23 

,00577 

23.83 

3 

141.6 

109.9 

1125.1 

1015.3 

7325 

117.93 

.00848 

21.78 

4 

153.1 

121.4 

1128.6 

1007.2 

5588 

89.8J 

.01112 

19.74 

5 

1623 

130.7 

1131.4 

1000.7 

4530 

72.50 

.01373 

17.70 

6 

170.1 

138.6 

11338 

91*5.2 

3816 

61.10. 

.01631 

15.67 

7 

176.9 

145.4 

1135  9 

990.5 

3302 

53.00 

.01887 

13.63 

8 

1829 

151  5 

1137.7 

986.2 

2912 

46.60 

,02140 

11.60 

9 

188.3 

156.9 

1139.4 

982.4 

2607 

41.82 

,02391 

9.56 

10 

193.2 

161.9 

1140.9 

979.0 

2361 

37.80 

.02641 

7.52 

11 

197.8 

166.5 

11423 

975.8 

2159 

34.61 

.02889 

549 

12 

202.0 

170.7 

1143.5 

972.8 

1990 

31.90 

.03136 

3.45 

13 

2)5.9 

174.7 

1144.7 

970.0 

1846 

29.58 

.03381 

1.41 

14 

209.6 

178.4 

1145.9 

967.4 

1721 

27.50 

.03G25 

Gauge 

Pressure 
Ibs.  per. 

14.7 

212 

180.9 

1146.6 

965.7 

1646 

26.36 

.03794 

SQ.  in. 

0.304 

15 

213.0 

181.9 

1146.9 

965.0 

1614 

25,87 

,03868 

13 

16 

216.3 

1853 

1147.9 

96?  7 

1519 

21.33 

.04110 

2.3 

17 

219.4 

188.4 

1148  9 

9605 

14^4 

22.98 

.04352 

33 

18 

222.4 

191.4 

1149.8 

958  3 

1359 

21.78 

.04592 

4.3 

19 

225.2 

194.3 

1150  6 

956.3 

1292 

20.70 

.04831 

53 

20 

227.9 

197.0 

1151.5 

954.4 

1231 

19.72 

.05070 

6.3 

21 

230.5 

199.7 

1152  2 

952.6 

1176 

18.84 

.05308 

7.3 

22 

2330 

202.2 

11530 

95J.8 

1126 

18.03 

.05545 

8.3 

23 

235.4 

204.7 

.7 

949.  1 

1080 

17.30 

,05782 

9.3 

24 

237.8 

207.0 

1154.5 

947.4 

1038 

16.62 

.06018 

10.3 

25 

240.0 

2093 

1155.1 

945.8 

998.4 

15.99 

.06253 

11.3 

26 

242.2 

211.5 

.8 

944.3 

962  3 

15.42 

,00487 

12.3 

27 

244.3 

213.7 

1156.4 

942.8 

928.8 

14.88 

,06721 

13.3 

28 

246  3 

215.7 

1157.1 

941.3 

897.6 

14.38 

.06955 

143 

29 

2483 

217.8 

,7 

9399 

868.5 

13.91 

.07188 

15.3 

30 

250.2 

219.7 

lir»8.3 

938.9 

841.3 

13.48 

.07420 

*  Reprinted,  by  permission,  from  POWER  CATECHISM.  •! 


PROPERTIES  OF  SATURATED  STEAM. 


677 


Gauge  Pressure. 
Ibs.  per  sq.  in. 

Absolute  Press- 
ure. Ibs.  per 
square  inch. 

Temperature 
Fahrenheit. 

Total  Heat 
above  32°  F. 

tLl 
It! 

G^S 

I"1 

Relative  Volume 
Vol.  of  Water 
at39°F.  =  1. 

VolumeCu.ft. 
in  1  Ib.  of  Bteam. 

is 

51 

15 
•&$ 
£ 

In  the 
Water 
Ji 
Heat- 
units. 

In  the 
Steam 

Heat 

units. 

16.3 

31 

252.1 

2216 

.8 

937.2 

815.8 

13.07 

.07652 

17.3 

32 

254.0 

223.5 

1159.4 

935.9 

791.8 

12.68 

.07884 

18.3 

33 

255.7 

2253 

.9 

934.6 

769.2 

12  32 

.08115 

19.3 

34 

257.5 

227.1 

1160.5 

933.4 

748.0 

11.98 

.08346 

20.3 

35 

2592 

228.8 

1161.0 

932.2 

727.9 

11.66 

.08576 

21.3 

36 

260.8 

230.5 

.5 

931.0 

708.8 

11.36 

.08806 

22.3 

37 

262.5 

232.1 

1162.0 

929.8 

690.8 

11.07 

.09035 

23.3 

38 

264.0 

2338 

.5 

928.7 

673.7 

10.79 

.09264 

24.3 

39 

265.6 

235.4 

.9 

927.6 

657.5 

10.53 

.09493 

25.3 

40 

267  1 

236.9 

1163.4 

926.5 

642.0 

10.28 

.09721 

263 

41 

268.  (i 

238.5 

.9 

925.4 

627.3 

10.05 

.09949 

27.3 

42 

270.1 

240.0 

1164.3 

924.4 

613.3 

9.83 

.1018 

28.3 

43 

271.5 

2414 

.7 

923.3 

599.9 

9.61 

.1040 

29.3 

44 

272.9 

242.9 

1165.2 

922.3 

587.0 

9.41 

.1063 

30.3 

45 

274.3 

244.3 

.6 

921.3 

574.7 

9.21 

.1086 

31.3 

46 

275.7 

245.7 

1166.0 

920.4 

563.0 

9.02 

.1108 

32  3 

47 

277.0 

247.0 

.4 

919.4 

551.7 

8.84 

.1131 

33.3 

48 

278,3 

2484 

.8 

918.5 

540.9 

8.67 

.1153 

34.3 

49 

279.6 

249.7 

1167.2 

917.5 

530.5 

8.50 

.1176 

35.3 

50 

280.9 

251.0 

.6 

916.6 

520.5 

8.34 

.1198 

36.3 

51 

282  1 

252.2 

1168.0 

915.7 

510.9 

8.19 

1221 

37.3 

52 

283  3 

253.5 

.4 

914.9 

501.7 

8.04 

1243 

38.3 

53 

2845 

254.7 

.7 

914.0 

492.8 

7.90 

.1266 

39.3 

54 

285.7 

256.0 

1169.1 

913.1 

484.2 

7.76 

1288 

40.3 

55 

286.9 

257.2 

.4 

'912.3 

475.9 

7.63 

1311 

41.3 

56 

288  1 

258.3 

.8 

911  5 

467.9 

7.50 

.1333 

42.3 

57 

289.1 

259.5 

1170.1 

910.6 

460.2 

7.38 

.1355 

43.3 

58 

290.3 

260.7 

.5 

909.8 

452.7 

7.26 

.1377 

44.3 

59 

291.4 

261.8 

.8 

9U9.0 

445.5 

7.14 

.1400 

45.3 

60 

292.5 

262.9 

1171.2 

908.2 

438.5 

7.03 

.1422 

463 

61 

293.6 

264.0 

.5 

907.5 

431.7 

6.92 

.1444 

47.3 

62 

294.7 

265  1 

.8 

906.7 

425.2 

6.82 

.1466 

48.3 

63 

295.7 

2662 

1172.1 

905.9 

418.3 

6.72 

.1488 

49.3 

64 

296.8 

267.2 

.4 

905.2 

412.  3 

6.62 

.1511 

50.3 

65 

297.8 

268.3 

.8 

904.5 

406.6 

6.53 

.1533 

51.3 

66 

298.8 

269.3 

1173.1 

903.7 

400.8 

6.43 

.1555 

52.3 

67 

299.8 

270.4 

.4 

903.0 

395.2 

6.34 

.1577 

53.3 

68 

300.8 

271.4 

.7 

9  2.3 

389.8 

6.25 

.1599 

54.3 

69 

301.8 

272.4 

1174.0 

901.6 

384.5 

6.17 

.1621 

55.3 

70 

3027 

273.4 

.3 

900.9 

379.3 

6.09 

.1643 

56.3 

71 

303.7 

274.4 

.6 

900  2 

374.3 

6.01 

.1665 

57.3 

72 

304.6 

275.3 

.8 

8995 

369.4 

5.93 

.1687 

68.3 

73 

305.6 

2763 

1175.1 

8989 

364.6 

6.85 

.1709 

59.3 

74 

306.5 

277.2 

.4 

898.2 

360.0 

5.78 

.1731 

678 


PROPERTIES  OF  SATURATED  STEAM. 


2  - 

m 

Total    Heat 

K3 

o> 

a  t_i  . 

4JS 

3 

g.3 

1M 

*d 

above  32  =  F. 

*>     .  02 

$?•<£.•£ 

|ln 

~J 

°5 

©  ^* 

£  .S 

-5  ® 
H 

In   the 

In    the 

fitl 

&* 

^2 
•  ^ 

*o| 

4> 

^.c© 

££ 

Water 

SSteam 

"S^-S 

?*cn 

<D  u 

-^  <D 

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oft 

,2  •  ^ 

c£ 

h 

H 

liiS 

S_;S 

1:2 

5^ 

F 

J<P  ^ 
B* 
•^ 

J* 

Heat- 
units- 

Heat- 
units, 

£«H 

Pa 

M 

£d 

°£-tJ 
^ 

60.3 

75 

307.4 

278.2 

.7 

897.5 

355.5 

5.71 

.1753 

61.3 

76 

308.3 

279.1 

1176.0 

896.9 

351.1 

5.63 

.1775 

62.3 

77 

309.2 

280.0 

.2 

896.2 

346.8 

5.57 

.1797 

63.3 

78 

310.1 

280.9 

.5 

895.6 

342.6 

5.50 

.1810 

64.3 

79 

310.9 

281.8 

.8 

895.0 

338.5 

5.43 

.1840 

65.3 

80 

311.8 

282.7 

1177.0 

894.3 

334.5 

5.37 

.1862 

66.3 

81 

312.7 

283.6 

.3 

893.7 

330.6 

5.31 

.1884 

67.3 

82 

313.5 

284.5 

.6 

893.1 

326.8 

5.25 

.1906 

68.3 

83 

314.4 

285.3 

.8 

892.5 

323.1 

5.18 

.1928 

69.3 

84 

315.2 

286.2 

1178.1 

891.9 

319.5 

5.13 

.1950 

70.3 

85 

316.0 

287.0 

.3 

891.3 

315.9 

5.07 

.1971 

71.3 

86 

316.8 

287.9 

.6 

890.7 

312.5 

5.02 

.1993 

72.3 

87 

317.7 

288.7 

.8 

890.1 

309.1 

4.96 

.2015 

73.3 

88 

318.5 

289.5 

1179.1 

889.5 

305.8 

4.91       .2036 

74.3 

89 

319.3 

290.4 

.3 

888.9 

302.5 

4.86 

.2058 

75.3 

90 

320.0 

291.2 

.6 

888.4 

299.4 

4.81 

.2080 

76.3 

91 

320.8 

292.0 

.8 

887.8 

296.3 

4.76 

.2102 

77.3 

92 

321.6 

292.8 

1180.0 

887.2 

293.2 

4.71 

.2123 

78.3 

93 

322.4 

293.6 

.3 

886.7 

290.2 

4.66 

.2145 

79.3 

94 

323.1 

294.4 

.5 

886.1 

287.3 

4.62 

.2166 

80.3 

95 

323.9 

295.1 

.7 

885.6 

284.5 

4.57 

.2188 

81.3 

96 

324.6 

295.9 

1181.0 

885.0 

281.7 

4.53 

.2210 

82.3 

97 

325.4 

296.7 

.2 

884.5 

279.0 

4.48 

.2231 

83.3 

98 

326.1 

297.4 

.4 

884.0 

276.3 

4.44 

.2253 

84.3 

99 

326.8 

298.2 

.6 

883.4 

273.7 

4.4.0 

.2274 

85.3 

100 

327.6 

298.9 

.8 

882.9 

271.1 

4.36 

.2296 

86.3 

101 

328.3 

299.7 

1182.1 

882.4 

268.5 

4.32 

.2317 

87.3 

102 

329.0 

300.4 

.3 

881.9 

266.0 

4.28 

.2339 

88.3 

103 

329.7 

301.1 

.5 

881.4 

263.6 

4.24 

.2360 

89.3 

104 

330.4 

301.9 

.7 

880.8 

261.2 

4.20 

.2382 

90.3 

105 

331.1 

302.6 

.9 

880.3 

258.9 

4.16 

.2403 

91.3 

106 

331.8 

303.3 

1183.1 

879.8 

256.6 

4.12 

.2425 

92.3 

107 

332.5 

304.0 

.4 

879.3 

254.3 

4.09 

.2446 

93.3 

108 

333.2 

304.7 

.6 

878.8 

252.1 

4.05 

.2467 

94.3 

109 

333.9 

305.4 

.8 

878.3 

249.9 

4.02 

.2489 

95.3 

110 

334.5 

306.1 

1184.0 

877.9 

247.8 

3.98 

.2510 

96.3 

111 

335.2 

306.8 

.2 

877.4 

245.7 

3.95 

.2531 

97.3 

112 

335.9 

307.5 

.4 

876.9 

243.6 

3.92 

.2553 

98.3 

113 

336.5 

308.2 

.6 

876.4 

241.6 

3.88 

.2574 

99.3 

114 

337.2 

308.8 

.8 

875.9 

239.6 

3.85 

.2596 

100.3 

115 

337.8 

309.5 

1185.0 

875.5 

237.6 

3.82 

.2617 

101.3 

116 

338.5 

310.2 

.2 

875.0 

235.7 

3.79 

.2638 

7.02.3 

117 

339.1 

310.8 

.4 

874.5 

233.8 

3.76 

.2f,60 

PROPERTIES  OF  SATURATED  STEAM. 


679 


£  ' 

03 

I      Total    Heat 

. 

C  H 

,-S     i 

©  tn  rj 

o*- 

above  32s  F. 

.U        03 

12 

L-^ 

ft 

£2j 

5  o 

32 
U 

||ii 

If 

?| 

In  the 

In  the 

—  M 
O 

e.c  2 

2*53 

Water 

h 

Ste-'in 

5  II  © 

icir 

|J 

il 

11 

O 

Jig 

•"i 

Jh 

Heat- 
units. 

Heat- 
units. 

©  ii  ,  t 

r 

~t*—  * 

*3 

P 

103.3 

118 

339.7 

311.5 

.6 

874.1 

231.9 

3.73 

.2C81 

104.3 

119 

340.4 

312.1 

.8 

873.6 

230.1 

3.70 

.2703 

105.3 

120 

341.0 

312.8 

.9 

873.2 

228.3 

3.67 

.2724 

106.3 

121 

341.6 

313.4 

1186.1 

872.7 

226.5 

3.64 

.2745 

107.3 

122 

342.2 

314.1 

.3 

872.3 

224.7 

3.62 

.2760 

108.3 

123 

342.9 

314.7 

.5 

871.8 

223.0 

3.19 

.2788 

109.3 

124 

343.5 

315.3 

.7 

871.4 

221.3 

3.50 

.2809 

110.3 

125 

344.1 

316.0 

.9 

870.9 

219.6 

3.53 

.2830 

111.3 

126 

344.7 

316.6 

1187.1 

870.5 

218.0 

3.51 

.28C1 

112.3 

127 

345.3 

317.2 

.3 

870.0 

216.4 

3.48 

,2872 

113.3 

128 

345.9 

317.8 

.4 

869.6 

214.8 

3.46 

.2894 

114.3 

129 

346.5 

318.4 

.6 

869.2 

213.2 

3.43 

.2915 

115.3 

130 

347.1 

319.1 

.8 

868.7 

211.6 

3.41 

.2936 

116.3 

131 

347.6 

319.7 

1188.0 

868.3 

210.1 

3.38 

.2957 

117.3 

132 

348.2 

320.3 

.2 

867.9 

208.6 

3.36 

.2978 

118.3 

133 

348.8 

320.8 

.3 

867.5 

207.1 

3.33 

.3000 

119.3 

134 

349.4 

321.5 

.5 

867.0 

205.7 

3.31 

.3021 

120.3 

135 

350.0 

322.1 

.7 

866.6 

204.2 

3.29 

.3042 

121.3 

136 

350.5 

322.6 

.9 

866.2 

202.8 

3.27 

.3063 

122.3 

137 

351.1 

323.2 

lisy.o 

865.8 

201.4 

3.24 

.3084 

123.3 

138 

351.8 

323.8 

.2 

865.4 

200.0 

3.22 

.3105 

124.3 

139 

352.2 

324.4 

.4 

865.0 

198.7 

3.20 

.3126 

125.3 

140 

352.8 

325.0 

.5 

864.6 

197.3 

3.18 

.3147 

126.3 

141 

353.3 

325.5 

.7 

864.2 

196.0 

3.16 

.3169 

127.3 

142 

353.9 

326.1 

.9 

863.8 

194.7 

3.14 

3190 

128.3 

143 

354.4 

326.7 

1190.0 

863.4 

193.4 

3.11 

.3211 

129.3 

144 

355.0 

327.2 

.2 

863.0 

192.2 

3.09 

.3232 

130.3 

145 

355.5 

327.8 

.4 

862.6 

190.9 

3.07 

.3253 

131.3 

146 

356.0 

328.4 

.5 

862.2 

189.7 

3.05 

.3274 

132.3 

147 

356.6 

328.9 

.7 

861.8 

185.5 

3.04 

.3295 

133.3 

148 

357.1 

329.5 

.9 

861.4 

187.3 

3.02 

.331f 

134.3 

149 

357.6 

330.0 

1191.0 

861.0 

186.1 

3.00 

.3331 

135.3 

150 

358.2 

330.6 

.2 

860.6 

184.9 

2.98 

.3358 

136.3 

151 

358.7 

331.1 

.3 

860.2 

183.7 

2.96 

.3379 

137.3 

152 

359.2 

331.6 

.6 

859.9 

182.6 

2.94 

.3400 

138.3 

153 

359.7 

332.2 

.7 

859.5 

181.5 

2.92 

.3421 

139.3 

154 

360.2 

332.7 

.8 

859.1 

180.4 

2.91 

.3442 

140.3 

155 

360.7 

333.2 

1192.0 

858.7 

179.2 

2.89 

.3463 

141.3 

156 

361.3 

333.8 

.1 

858.4 

178.1 

2.87 

.3483 

142.3 

157 

361.8 

334.3 

.3 

858.0 

177.0 

2.85 

.3504 

143.3 

158 

362.3 

334.8 

.4 

857.6 

175.0 

2.84 

.3525 

144.3 

159 

362.8 

335.3 

.6 

857.2 

174.9 

2.82 

.3546 

145.3 

160 

363.3 

335.9 

.7 

856.9 

173.9 

2.80 

3567 

68o 


PROPERTIES  OF  SATURATED  STEAM. 


2"a     ' 

®  .            Total  Heat 

^ 

i*vs 

siS 

^ 

!"• 

gfc-g 

above  32  °  F. 

"£•*:§ 

•2  tell 

01 

5  .0 

©  x 

PH      2 

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®  1   ^ 

t>P^  • 

CJ32 

c  S 

^s 

||  2. 

£-4     " 

In   the 

In  the 

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«-. 

c*3 

P<   2 

Water 

Steam 

•§7? 

®  ^*CJ 

S  • 

"i3nn 

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h 

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03  l-i  C* 
,Q  p  Cfi 

*PM 

Heat- 

Heat- 

-2    K 

J^>~c3 

C  »H 

>£ 

<§a 

! 

units. 

units. 

^ 

& 

'- 

146.3 

161 

363.8 

336.4 

.9 

856.5 

172.9 

2.79 

.3588 

147.3 

162 

364.3 

336.9 

1193.0 

856.1 

171.9 

2.77 

.3609 

148.3 

163 

364.8 

337.4 

.2 

855.8 

171.0 

2.76 

.3630 

149.3 

164 

365.3 

337.9 

.3 

855.4 

170.0 

2.74 

.3650 

150.3 

165 

365.7 

338.4 

.5 

855.1 

169.0 

2.72 

.3671 

151.3 

166 

366.2 

338.9 

.6 

854.7 

168.1 

2.71 

.  3692 

152.3 

167 

366.7 

339.4 

.8 

854.4 

167.1 

2.69 

.3713 

153.3 

168 

367.2 

339.9 

.9 

854.0 

166.2 

2.68 

.3734 

154.3 

169 

367.7 

340.4 

1194.1 

853.6 

165.3 

2.C6 

.3754 

155.3 

170 

368.2 

340.9 

.2 

853.3 

164.3 

2.65 

.3775 

156.3 

171 

368.6 

341.4 

.4 

852.9 

163.4 

2.C3 

.3796 

157-3 

172 

369.1 

341.9 

.5 

852.6 

162.5 

2.62 

.3817 

158.3 

173 

369.6 

342.4 

.7 

852.3 

161.6 

2.61 

.3838 

159.3 

174 

370.0 

342.9 

.8 

851.9 

160.7 

2.59 

.3858 

160.3 

175 

370.5 

343.4 

.9 

851.6 

159.8 

2.58 

.3879 

161.3 

176 

371.0 

343.9 

1195.1 

851.2 

158.9 

2.56 

.3900 

162.3 

177 

371.4 

344.3 

.2 

850.9 

158.1 

2.55 

.3921 

163.3 

178 

371.9 

344.8 

.4 

850.5 

157.2 

2.54 

.3942 

1C4.3 

179 

372.4 

345.3 

.5 

850.2 

156.4 

2.52 

.3962 

165.3 

180 

372.8 

345.8 

.7 

849.9 

155.6 

2.51 

.3983 

166.3 

181 

373.3 

346.3 

.8 

849.5 

154.8 

2.50 

.4004 

167.3 

182 

373.7 

346.7 

.9 

849.2 

154.0 

2.48 

.4025 

168.3 

183 

874.2 

347.2 

.1 

848.9 

153.2 

2.47 

.4046 

169.3 

184 

374.6 

347.7 

1196.2 

848.5 

152.4 

2.46 

.4066 

170.3 

185 

375.1 

348  1 

.3 

848.2 

151.6 

2.45 

.4087 

171.3 

186 

375.5 

348.6 

.5 

847.9 

150.8 

2.43 

.4108 

172.3 

187 

375.9 

349.1 

.6 

847.6 

150.  0 

2.42 

.4129 

173.3 

188 

376.4 

349.5 

.7 

847.2 

149.2 

2.41 

.4150 

174.3 

189 

376.9 

oSO.O 

.9 

846.9 

148.5 

2.40 

.4170 

175.3 

190 

377.3 

350.4 

1197.0 

846.6 

147.8 

2.39 

.4191 

176  3 

191 

377.7 

350.9 

.1 

846.3 

147.0 

2.37 

.4212 

177.3 

192 

378.2 

351.3 

.3 

845.9 

14G.3 

2.36 

.4233 

178.3 

193 

378.6 

::51.8 

.4 

845.6 

145.6 

2.C5 

.4254 

179.3 

194 

379.0 

352.2 

.5 

845.3 

144.9 

2.34 

.4275 

180.3 

195 

379.5 

352.7 

.7 

845.0 

144.2 

2.33 

.4296 

181.3 

196 

380.0 

353.1 

.8 

844.7 

143.5 

2.12 

.4317 

182.3 

197 

380.3 

353.6 

C] 

844.4 

142.8 

2.:i 

.4337 

183.3 

198 

380.7 

354.0 

1198  !l 

844.1 

142.1 

2.29 

.4358 

184.3 

199 

381.2 

354.4 

.2 

843.7 

141.4 

2.28 

.4379 

185.3 

200 

381.6 

354.9 

c 

843.4 

140.8 

2.27 

.4400 

186.3 

201 

382.0 

355.3 

m4 

843.1 

140.1 

2.26 

.4-120 

187.3 

202 

382.4 

355.8 

.6 

842.8 

139.5 

2.25 

.4441 

188.3 

203 

382.8 

356.2 

.7 

842.5 

133.8 

2.2i 

.4462 

PROPERTIES  OF  SATURATED  STEAM. 


681 


Si 

en 

o5«-r2 

££§ 

<D    . 

^"S 

s'S 

Total 

above  . 

Heat 

12°  F. 

^ 

+3            W 

«j-'±i 

0>-kJ 

12. 

2    C»H 

.jS 
-3 

§5 

ii 

¥ 

Absolute  I 
ure.  Ibs.  ] 
square  in 

Tomperat 
Fahreuh 

In  the 
\\ater 
h 
Heat- 
units. 

In  the 
B,er 

Heat- 
units. 

<D~-  0 

tc  1  P 

*""*  4-s 

c      ^ 
©il  ® 

a 

£i" 
K? 

1? 

Volume  Ci 
in  lib.  of  b 

Weight  of 
ft.  Steam, 

189.3 

204 

383.2 

356.6 

.8 

842.2 

138.1 

2.23 

.4482 

190.3 

205 

383.7 

357.1 

1199.0 

841.9 

137.5 

2.22 

.4503 

191.3 

206 

381.1 

357.5 

.1 

841.6 

136.9 

2.21 

.4523 

192.3 

207 

384.5 

357.9 

.2 

841.3 

136.3 

2.20 

,454i 

193.3 

208 

384.9 

358.3 

.3 

841.0 

135.7 

2.19 

.4564 

194.3 

209 

385.3 

358.8 

.5 

840.7 

135.1 

2.18 

.4585 

195.3 

210 

385.7 

359.2 

.6 

840.4 

134.5 

2.17 

.4605 

196.3 

211 

386.  1 

359.6 

.7 

840.1 

133.9 

2.16 

.4626 

197.3 

212 

386.5 

360.0 

.8 

839.8 

133.3 

2.15 

.4646 

198.3 

213 

380.  9 

360.4 

.9 

839.5 

132.7 

2.14 

.4667 

199.3 

21i 

3H7.3 

360.9 

1200.1 

839.2 

132.1 

2.13 

.4687 

200.3 

215 

387.7 

361.3 

.2 

838.9 

131.5 

2.12 

.4707 

201.3 

216 

388.1 

361.7 

.3 

838.6 

130.9 

2.12 

.4728 

202.3 

217 

388.5 

362.1 

.4 

838.3 

130.3 

2.11 

.4748 

203.3 

218 

388.9 

362.5 

.6 

838.1 

129.7 

2.10 

.4768 

204.3 

219 

389.3 

362.9 

.7 

837.8 

129.2 

2.09 

.4788 

205.3 

220 

389.7 

362.2* 

1200.8 

838.6* 

128.7 

2.06 

.4852 

215.3 

230 

393.6 

360.2 

1202.0 

835.8 

123.3 

1.98 

.5061 

225.3 

210 

397.3 

370.0 

1203.1 

833.1 

118.5 

1.90 

.5270 

235.3 

250 

400.9 

373.8 

1204.2 

830.5 

114.0 

1.83 

.5478 

245.3 

260 

404.4 

377.4 

1205.3 

827.9 

109.8 

1.76 

.5686 

255.3 

270 

407.8 

380.9 

1206.3 

825.4 

105.9 

1.70 

.5894 

265.3 

280 

411.0 

381.3 

1207.3 

823.0 

102.3 

1.64 

.6101 

275.3 

290 

414.2 

387.7 

1208.3 

820.6 

99.0 

1.585 

.6308 

285.3 

300 

417.4 

390.9 

1209.2 

818.3 

95.8 

1.535 

.6515 

335.3 

350 

43'J.O 

40G.3 

1213.7 

807.5 

82.7 

1.325 

.7515 

385.3 

400 

41-1.9 

419.8 

1217.7 

797.9 

72.8 

1.167 

.8572 

435.3 

450 

456.6 

432.2 

1221.3 

789.1 

65.1 

1.042 

.9595 

485.3 

500 

467.4 

443.5 

1224.5 

781.0 

58.8 

.942 

1.062 

535.3 

550 

477.5 

451.1 

1227.6 

773.5 

53.6 

.859 

1.164 

585.3 

600 

486.9 

464.2 

1230.5 

766.3 

49.3 

.790 

1.266 

635.3 

650 

495.7 

473.6 

1233.2 

759.6 

45.6 

.731 

1.368 

685.3 

700 

504.1 

482.4 

1235.7 

753.3 

42.4 

.680 

.470 

735.3 

7CO 

512.1 

490.9 

1238.0 

747.2 

39.6 

.636 

.572 

785.5 

800 

519.6 

49M.9 

1240.3 

741.4 

37.1 

.597 

.674 

835.3 

850 

526.8 

506.7 

1242.5 

735.8 

34.9 

.563 

.776 

885.3 

900 

533.7 

514.0 

1244.7 

730.6 

33.0 

.532 

.878 

<i:r>..'{ 

950 

540.3 

521.3 

1246.7 

725.4 

31.4 

.505 

.080 

985.3 

1000 

546.8 

528.3 

1248.7 

720.3 

30.0 

.480 

2.082 

*The  discrepancies  at  205.3  Ibs.  gauge  are  due  to  the  change  from  Dery's  to  Duel's 
figures. 


682  APPENDIX. 


Appendix 


QUESTIONS  ON  THE  SUBJECT  MATTER  OF  PART  I, 
WITH  PAGE  REFERENCES. 

CHAPTER  I. 

Principal  Materials  of  Engineering  Construction. 

PAGE. 

What  are  the  chief  properties  and  uses  of  aluminum? i 

What  are  the  chief  properties  and  uses  of  antimony? i 

What  are  the  chief  properties  and  uses  of  bismuth? 2 

What  are  the  chief  properties  and  uses  of  copper? 2 

How  does  heat  affect  the  tensile  strength  of  copper? 2 

Describe  the  operation  of  brazing 2 

What  is  meant  by  burning  copper? 2 

What  is  cast  iron? 4 

What  are  gray,  white  and  mottled  irons? 4 

WThat  is  meant  by  combined  and  by  graphitic  carbon? 4 

What  is  the  influence,  of  silicon  on  cast  iron? 5 

What  is  a  chilled  cast  iron? 6 

What  is  the  influence  of  sulphur  on  cast  iron? 6 

What  is  the.  influence  of  manganese  on  cast  iron? 7 

What  is  the  influence  of  chromium  on  cast  iron? 7 

What  is  the  shrinkage  of  cast  iron? 7 

On  what  is  the  hardness  of  cast  iron  chiefly  dependent? 7 

On  what  is  the  strength  of  cast  iron  chiefly  dependent? 7 

What  are  the  chief  uses  of  cast  iron  in  marine  engineering? 8 

What  chief  points  are  to;  be  kept  in  mind  in  the  inspection  of  cast- 
ings ?    8 

What  is  malleable  iron  and  how  is  it  made? 9 

What  are  its  properties  and  uses  in  marine  engineering? 10 

What  is  wrought  iron  and  how  is  it  made? 10 

What  is  the  effect  of  sulphur  on  wrought  iron? .'  n 

What  is  the  effect  of  phosphorus  on  wrought  iron? u 

What  special  properties  has  wrought  iron? n 

Describe  the  operation  of  welding n 

What  are  its  chief  uses  in  marine  engineering? n 

What  is  steel  ? .  12 

Describe  briefly  the  Bessemer  and  Open-hearth  processes 13,  14 

Compare   the   two   products 14 

What  is  the  influence  of  sulphur  on  steel? 15 

What  is  the  influence  of  phosphorus  on  steel? 15 

What  is  the  influence  of  silicon  on  steel? 15 

What  is  the  influence  of  manganese  on  steel? 15 

What  is  semi  steel  ? 16 

What  are  the  leading  mechanical  properties  of  steel? 16 

What  special  properties  has  steel? 21 

Describe  the  operation  of  tempering 22 

What  is  nickel   steel  ? 22 

What  is  chrome  steel?. 23 

What  is  tungsten  steel?   23 

What  are  the  chief  uses  of  steel  in  marine  engineering?   23 


APPENDIX.  683 

PAGE. 

What  are  the  chief  properties  and  uses  of  lead? 23 

What  are  the  chief  properties  and  uses  of  tin? 24 

What  are  the  chief  properties  and  uses  of  zinc?  24 

What  is  an  alloy? 24 

What  are  the  proportions  of  some  common  alloys? 25 

To  what  tests  are  metals  subjected? 26 

What  is  meant  by  the  terms  ultimate  strength,  elastic  limit,  elongation, 

reduction  of  area  ? 26 

Wlnt  forms  of  test  pieces  are  employed,  and  how  are  the  various 

tests  carried  out? 28,  29 

CHAPTER  II. 

Fuels. 

What  are  the  chief  constituents  of  coal? 31 

What  are  the  chief  varieties  of  coal? 31 

What  are  about  the  proportions  of  volatile  matter  and  carbon  in  the 

different  varieties  ? 32 

What  per  cent  of  ash  is  usually  found  in  good  coal? 32 

Describe  briefly  the  process  of  combustion  with  anthracite  coal  and 

with  bituminous  or  semi-bituminous  coal 32 

How  much  heat  is  liberated  by  the  complete  combustion  of  I  Ib.  of 

carbon  ?  32 

How  much  for  T  Ib.  of  hydrogen? 32 

How  much  air  is  required  to  barely  furnish  the  oxygen  necessary  for 

the  combustion  of  an  average  Ib.  of  coal? 33 

How  much  is  actually  required  and  why  is  the  excess  necessary?.  ...  33 

What  is  soot  and  how  is  it  formed? 33 

What  is  clinker  and  how  is  it  formed? 35 

What  is  meant  by  the  weathering  of  coal? 36 

What  influence  does  iron  pyrites  have  on  weathering? 37 

What  is  spontaneous  combustion  and  what  are  the  conditions  on 

which  it  depends? 37 

How  many  cubic  feet  bunker  space  are  usually  allowed  per  ton 

of  coal  ? 40 

What  are  briquettes?. 41 

What  are  the  constituents  of  liquid  fuel? 42 

What  are  the  conditions  for  the  combustion  of  liquid  fuel? 43 

What  are  the  conditions  affecting  the  likelihood  of  the  explosion  of 

gases  arising  from  liquid  fuel? 44 

How  does  the  evaporative  power  of  liquid  fuel  compare  with  that 

of  coal  ? 44 

What  are  the  chief  advantages  of  liquid  fuel? 45 

What  is  the  present  chief  difficulty  attending  the  extended  use  of 

liquid  fuel  ? 46 

CHAPTER  III. 

Boilers. 

What  are  the  two  fundamental  types  of  boilers? 48 

]nto  what  classes  may  fire-tube  boilers  be  divided? 49 

•  Give  a  general  description  of  these  various  classes 50 

Give  a  general  description  of  a  few  leading  types  of  water-tube 

boilers  53 

Compare  the  two  types  water-tube  and  fire-tube  as  regards  their 

advantages  and  disadvantages  for  marine  use 56 

In  what  way  may  a  riveted  joint  fail? 68 

What  is  meant  by  sinorle  and  double  shear?  77 

Describe  the  various  forms  of  riveted  joints,  and  show  how  they  may 

be  proportioned  so  as  to  give  approximately  equal  strenght  in 

plate  'and  rivet  section 71-86 


684  APPENDIX. 

PAGE. 

What  material  is  used  for  modern  boilers? 86 

Are  rivet  holes  usually  punched  or  drilled? 86 

Compare  the  relative  advantages  of  the  two  methods 86 

What  is  meant  by  caulking  a  joint  and  how  is  it  done? 87 

In  Scotch  boilers  what  form  of  joints  is  used  for  the  longitudinal 

seam?  what  for  the  circumferential  seams? 87 

Why   should  the   longitudinal   seams  have  a  higher   efficiency  than 

the  circumferential  ? 88 

What  is  the  relative  strength  of  the  boiler  to  resist  rupture  in  these 

two    directions? 88 

How  are  the  head  plates  usually  flanged? 88 

Describe  the  styles  of  corrugated  furnace  in  common  use 88 

Describe  various  modes  of  connection  between  the  furnace  and  the 

combustion    chamber 88 

What  are  the  two  usual  forms  of  combustion  chamber  top? 90 

How  are  the  tubes  secured  in  the  tube  sheet? 90 

What  are  stay  tubes  and  how  are  they  secured? 92 

What  is  the  Serve  tube  and  what  advantages  are  claimed  for  it?.  ...     93 

WThat  are  retarders  and  what  is  their  use? 93 

What  is  the  Admiralty  ferrule  and  what  is  its  use? 93 

What  fundamental  principles  govern  the  bracing  of  a  boiler? 94 

How  were  furnaces  stiffened  before  the  invention  of  the  corrugated 

form  ? 95 

Describe  the  various  forms  of  braces  used  in  modern  boilers,  and  the 

method  of  fitting  them  up 95 

Of  what  advantage  is  the  hollow  or  drilled  screw  stay  bolt? 98 

Describe  the  form  of  girder  or  crown  bar  with  which  the  top  of  the 

combustion  chamber  is  usually  supported 100 

What  is  a  man-hole  and  cover,  and  what  is  its  use? 101 

Give  approved  methods  of  fitting  them  up 101 

Describe  the  fitting  up  of  the  ordinary  furnace  door 103 

Describe  the  usual  form  of  grate  bar  and  the  methods  of  supporting 

it  in  the  furnace 104 

What  is  the  bridge  wall  and  how  is  it  fitted  up? 104 

Where  do  the  gases  pass  after  leaving  the  tubes?     106 

Describe  the  usual  style  of  front  connections  and  uptakes 106 

Describe  the  funnel  and  the  usual  method  of  fitting  it  up  106 

What  is  the  ratio  of  heating  surface  to  grate,  surface? 112 

How  is  the  horse  power  of  a  boiler  related  to  the  heating  surface  or 

to   the  weight? 112,  113 

Mention  the  various  boiler  mountings 115,   129 

Of  what  use  is  a  safety  valve? 115 

Name  the  principal  valves  on  a  boiler 115,  127 

Describe  the  U.  S.  Standard  safety  valve 115 

Describe  the  usual  type  of  spring  safety  valve 116 

What  is  a  muffler  and  what  is  its  use? 118 

What  is  the  use  of  the  boiler  main  stop  valve? 118 

What  is  an  automatic  closing  valve,  and  what  is  its  use? 118 

What  is  the  dry-pipe  and  how  is  it  fitted  up? 120 

Describe  the  usual  form  of  boiler  check  valve 121 

What  are  the  bottom  and  surface  blows  and  how  are  they  fitted?.  . .  .    122 

Describe  the  usual  form  of  Bourdon  steam  gauge 124 

Describe    the   usual   manner   of   fitting   up    water    cocks   and    water 

gauges 125 

What  is  a  hydrokineter  and  what  is  its  use? 127 

What  is  a  hydrometer  and  what  is  its  use? 127 

How  are  the  boilers  supported  in  the  ship? 128 

Describe  the  usual  forms  of  boiler  saddles 128 

To  what  is  draft  due? 129 

How  is  draft  measured? • 131 

What  are  the  chief  methods  in  use  for  increasing  the  draft? 132 


APPENDIX.  685 

PAGE. 

Describe    briefly    the    closed    stoke-hold    system — the    closed    ash-pit 

system — the  use  of  exhaust  fans  in  the  uptakes — and  of  jets  in  the 

base  of  the  funnel 133-137 

What  advantages  are  there   in   heating  the  air  introduced  into  the 

furnace's?    135 

Describe  briefly  the  Howden  system  of  forced  draft 133 

Describe  briefly  the  Ellis  &  Eaves  system  of  induced  draft 135 

(iive    ;he    U.    s.    rule    for   t!vj    pressure    allowed   on    cylindrical    shell 

boilers    138 

What    is   the    relation   between   the   test   pressure   and   the    working 

pressure   allowed? 138 

What   is  the  relation  between  the  thickness  of  butt  straps  and  the 

thickness   of   shell   plates ~J   138 

How  would  you  compute  the  size  of  stays  for  a  given  steam  pres- 
sure?   .139.  480 

How  would  you  compute  for  a  given  steam  pressure  the  thickness 

of  a  flat  plate  supported  by  stays? 139 

Give   rules   for  corrugated   furnace   flues 141,  142 

Give  rules  for  ribbed  furnace  flues 142 

What    are    the    proportions    for    flue    lining    subjected    to    external 

pressure?   144 

How  do  yon  compute  for  a  given  pressure  the  necessary  dimensions 

of  crown  bars? ' 145 

How  do  you  compute  the  thickness  of  a  bumped  head? 146 

How  do  you  determine  the  pressure  allowed  on  unstayed  flat  heads.  .    146 
How  do  you  determine  the  pressure  allowed  for  concave  heads?.  ..  .    147 

What  are  the  rules  for  fitting  manholes? 147 

What  are  the  rules  for  fitting  safety  plugs? 148 

•\t   what   temperature   does  a   safety  plug  melt? 24 

Whaf  are  the  rules  for  fitting  gauge  cocks? 148 

What    are  the   rules   for  fitting  safety  valves? 148 

What  considerations  govern  the  area  of  a  safety  valve? 115.  148 

How  would  you  compute  for  a  given  steam  pressure  the  thickness 

of  copper  steam   pipe? 150 

What  rules  govern  the  use  of  iron  and  steel  pipe? 150 

In   the  construction  of  coil  and  tubulous  boilers  what  provision   is 
made    for   the   use    of   cast    steel    manifolds,   tees,    return   bends 

and  elbows? 152 

What  special  rules  relate  to  the  construction  of  drums  for  tubulous 

boilers ?    152 

CHAPTER  IV. 

Marine  Engines. 

Explain  the  chief  characteristics  of  the  typical  marine  engine 154 

Explain  the  more  important  arrangements  which  may  be  made  of 

tin-  cylinders  and  cranks  of  multiple  expansion  engines 160 

Explain  the  chief  features  of  an  engine  cylinder 165 

What  is  a  liner  and  how  is  it  fitted? 165 

Explain  the  different  forms  of  cimine  columns  and  how  they  are 

titled  " 168 

flow  are  cylindrical  columns  braced  and  why? 171 

Explain  the  more  common  ways  of  fitting  up  the  guide  surface....  171 

Describe  the  usual  form  of  bed-nlate 772 

Describe  the  usual  form  of  engine  seating 174 

Describe  the  usual  form  of  marine  piston  with  its  packing  rings 

and  springs \-~ 

What  other  forms  of  piston  are  employed? 178 

What  is  the  purpose  of  the  piston  rod  and  how  is  it  fitted  up? 179 

Dc-cribe  the  various  styles  of  crosshead  to  be  met  with  in  marine 

practice    180 


636  APPENDIX. 

PAGE. 

Describe  the  various  styles  of  connecting  rod  to  be  found  in  marine 

practice    184 

Describe  the  built-up  and  the  solid  forged  styles  of  crank-shaft....   185 

What  are  the  advantages  of  making  shafting  hollow? 187 

To  what  extent  may  the  same  practice  be  applied  to  other  cylindrical 

members  ?  187 

Describe  the  usual  form  of  thrust  shaft 188 

How  is  the  propeller  or  tail  shaft  fitted  up  at  the  after  end,  and  how 
is  it  secured  to  the  length  of  shafting  next  forward  in  the  case 

of  twin  screws  ? 189 

Describe  the  usual  forms  of  crosshead  and  guide  bearings 190 

Describe  the  usual  form  of  bearing  for  the  crosshead  pins 191 

Describe  the  usual  form  of  bearing  for  the  crank-pin 192 

Describe  the  usual  form  of  bearing  for  the  crank-shaft 192 

Describe  the  usual  form  of  bearing  for  the  line  shaft 193 

Describe  the  two  leading  types  of  thrust  bearing 193 

Describe  the  usual  form  of  stern  and  bracket  bearings  196-10:9 

Describe  the  usual  type  of  western  river  boat  engine. 200 

What    are    the    essential    features    of    the    valve    gear    employed    on 

such  engines  ?   201 

What   is   a   western   river   boat    "doctor"? 204 

Describe  the  Parsons  steam  turbine 207 

What  are  its  advantages  and  disadvantages  for  marine  practice?.  ..  .  209 
What  is  the  office  of  the  throttle  valve,  and  what  forms  of  valve  may 

be  employed  for  this  purpose? 209 

What  is  the  office  of  the  main  stop  valve,  and  what  is  its  usual  form?  212 
Describe  the  usual  forms  of  globe,  angle  and  straightway  valves.  .213,  214 
What  is  the  office  of  the  cylinder  drain  and  relief  valves,  and  how 

are   they   usually   made?    215 

What  are  starting  valves?  216 

What  is  the  purpose  of  the  reversing  gear?   217 

Describe  the  "floating  lever"  type  of  reversing  gear   217 

What   other  forms   of  reversing   gear   are   employed? 219 

What  is  the  purpose  of  the  turning  gear,  and  what  are  its  main  fea- 
tures ? 220 

Describe  the  various  forms  of  packing  used  for  making  the  various 

fixed  joints  about  a  steam  engine    221 

Describe  the  more  common   forms  of  packing  used  in  the  piston- 
rod  and  valve  stem  stuffing  boxes    221,  224 

Wrhat  is  a  reheater,  and  what  is  its  purpose?  225 

What  is  the  office  of  the  governor?  225 

Describe  the  usual   principles   on   which   marine   governors   are   de- 
signed   225 

What  is  the  office  of  the  counter  gear,  and  of  what  does  it  consist?  227 
What  is  the  purpose  of  lagging  on  cylinders,  valve  chests,  etc.,  and 

how  is  it  usually  fitted  ?    .  . .  • 228 

What  kinds  of  oil  are  nsea  ior  luhncation,  and  what  are  their  special 

characteristics?     22g 

What  other  forms  of  lubricant  are  employed? 228 

At  what  point  in  a  bearing  should  the  lubricant  be  applied? 229 

About  how  much  lubricant  may  be  allowed  per  1,000  I.   H.   P.  per 

day  in  usual  practice  ? 229 

In  the  adjustment  of  the  bearing  how  much  clearance  may  be  left  be- 
tween the  journal  and  bearing  surface ? 236 

Describe  the  various  devices  in  use  for  distributing  oil  or  lubricant 

to  a  bearing   230-235 

Describe  the  leading  features  of  a  modern  system  of  oil  distribution  235 

What  are  the  principal  systems  of  piping  found  on  shipboard? 237 

What  materials  are  in  use  for  steam  and  water  piping? 237 

What  are  the  relative  advantages  of  copper,  wrought  iron  and  steel?  238 


APPENDIX.  687 

PAGE. 

What  is  the  purpose  of  an  expansion  joint? -' .  . .  239 

Describe  the  usual  form  of  expansion  joint 239 

CHAPTER  V. 

Auxiliaries. 

What  is  the  office  of  the  circulating  pump? 241 

Describe  the  usual  type  of  centrifugal  pump  and  explain  its  mode 

of   operation    241 

Describe  a  usual  type  of  outboard  discharge  valve   242 

Describe  the  usual  type  of  condenser 243 

1 1  ( >\v  are  condenser  tubes  packed  ?   245 

What  is  the  office  of  the  air  pumo?  245 

Describe   the   usual   type   of   construction   and   explain   its   mode   of 

operation    246 

What  are  the  relative  advantages  and  disadvantages  of  the  attached 

and  independent  forms  of  air  pump?   249 

Why  is  the  feed  pump  necessarily  of  different  type  from  the  circulat- 
ing pump?  251 

Describe  the  usual  form  of  attached  plunger  pump  and  explain  its 

mode  of  operation    251 

Why  is  the  area  of  the  steam-piston  larger  than  that  of  the  water 

plunger  ? 253 

What  is  the  common  ratio  between  these  two  areas? 236,  266 

Describe  a   common  form  of  injector  and  explain  the  principle  of 

its  operation   253 

What  is  the  difference  between  what  are  commonly  known  as  auto- 
matic injectors  and  inspirators?  255 

What  is  the  office  of  the  feed  heater? 255 

What  are  the  two  fundamental  types  of  heater? 255 

What  is  the  source  of  the  gain  in  the  case  of  heaters  using  the  fun- 
nel gases  as  a  source  of  heat?  255 

What  are  the  styles  of  feed  heater  using  steam  as  the  heating  agent?  256 
What  is  tlie  source  of  the  gain  in  the  case  of  heaters  using  steam  as 

the  source  of  the  heat ?  256,  259 

What  is  the  purpose  of  the  feed  water  filter? 260 

What  materials  are  used*  as  the  filtering  medium? 260 

What  is  the  purpose  of  the  evaporator,  and  of  what  does  it  consist?  261 
What  are  the  chief  points  to  be  observed  in  the  operation  of  the 

evaporator?  262 

Describe  a  standard  form  of  independent  feed  pump  and  explain  its 

mode  of  operation  26^ 

What  advantage  has  the  "Admiralty"  type  of  feed  pump  over 

other  forms?  2Q-. 

Wlni  are  the  uses  of  fans  or  blowers? 267 

Di-M-ribc  the  usual  form  of  centrifugal  fan  or  blower,  and  explain 

its  operation  26y 

What  is  the  office  of  the  separator?  .'.'.'.'.'  '  267 

Describe  a  usual  type  of  construction  ......  268 

Describe  the  ash  ejector  and  explain  its  mode  of  operation  ! ! .  '  ^fo 
What  principles  govern  the  general  arrangement  of  machinery  on  " 

shipboard?    '. f.  ...  272 

CHAPTER  VI. 

Operation,  Management  and  Repair. 

A  general  examination  of  the  boiler  and  fire-room  equipment  is  to 
be  made  previous  to  getting  up  steam.  Mention  the  more  im- 
portant points  to  be  attended  to  in  such  an  examination  273 


638  APPENDIX. 

PAGE. 

How  are  fires  laid  and  started?    274 

After  lighting  fires  what  points  may  receive  special  attention?  274,  275,  276 
What  precautions  should  be  taken  in  opening  a  valve  connecting  a 

boiler  with  a  pipe  in  which  there  is  no  steam  pressure? 275 

What  fundamental  points  should  be  kept  in  view  throughout  the  en- 
tire course  of  these  operations?   276 

What  steps  may  be  taken  when  s.team  is  formed  and  a  moderate 

pressure  is  developed  ?    276 

What  auxiliary  machinery  in  particular  should  receive  attention  at 

this    time  ?    276 

What  attention  should  be  paid  the  funnel  guys  during  this  period?  277 

Describe  briefly  the  routine  of  firing   277 

What  difference  of  method  may  be  employed  according  as  the  coal 

is    hard    or    soft  ? 277 

What  is  the  usual  thickness  of  the  fire?   278 

How  is  the  thickness  of  the  fire  related  to  the  draft  pressure? 278 

What  is  the  result  if  thin  spots  are  formed? 278 

What  means  are  available  for  working,  cleaning  and  caring  for  the 

fire  in  the  intervals  of  coaling? 278 

Describe  the  duties  of  the  water  tender  279 

Describe   the    "double    shut   off"    method   of   making   sure   that   the 

gauge  glass  is  clear   279 

For  what  purposes  is  blowing  off  now  employed? 281 

What  is  the  special  use  of  the  bottom  blow?     Of  the  surface  blow?  281 
How  may  a   plug  cock  be  tested  to   ascertain  whether   it   is   open 

or  closed  ?    281 

What  means  are  available  for  ascertaining  the  density  or  saturation 

of  the  water?    127,  282 

Describe  the  various  means  available  for  the  disposal  of  ashes..  .269,  282 

Describe  the  method  of  cleaning  a  fire   282 

What  means  are  available  for  removing  the  soot  and  ashes  which 

accumulate  in  the  tubes? 283 

What  preparations  are  made  for   sweeping  tubes,   and  how   is   the 

operation  carried  out? 283 

What  dispositions  may  be  taken  when  making  a  momentary  or  very 

short  stop  ? 284 

If  the  stop  is  to  be  of  longer  duration  what  dispositions  may  be 

necessary  or  suitable?  284 

What  principles  lie  at  the  foundation  of  these  various  steps? 285 

What  mode  of  firing  is  usually  most  effective  with  water-tube  boilers?  285 
Why  with  such  boilers  is  it  especially  necessary  to  pay  strict  attention 

"to  the  feed?  285 

What  trouble  is  met  with  on  the  fire   side  of  the  tubes  of  water- 
tube  boilers  ?  285 

What  dispositions  may  be  made  just  previous  to  coming  into  port,  or 
to  a  long  stop,  during  which  the  fires  are  to  be  hauled,  and  the 

boilers  opened  ? 286 

What  are  foaming  and  priming,  and  what  steps  may  be  taken  to  con- 
trol these  conditions? 287 

What  causes  may  affect  the  working  of  the  feed  pump,  and  what  steps 

may  be  taken  to  locate  and  remove  the  trouble? 288 

What  may  be  done  in  case  the  check  valve  is  jammed? 291 

What  may  be  done  in  case  the  water  gauge  glass  bursts?   291 

What  steps  may  be  taken  in  the  case  of  low  water  in  the  boilers?.  . . .  292 
What  steps  may  be  taken  in  the  case  of  collapse  or  rupture  of  fur- 
nace crowns  or  combustion  chambers? 294,  295 

What   steps   may  be   taken   in   the   case   of   serious    leakage   in   the 

boiler  tubes  ?  295 

What  steps  may  be  taken  in  the  case  of  a  ruptured  steam  pipe?.  ..  .   297 
What  are  the  first  steps  to  be  taken  in  connection  with  getting  under 

way  in  a  ship  with  whose  machinery  you  are  not  familiar? 298 


APPENDIX.  689 

PAGE. 

Mention    the    various    auxiliaries    which    must    be    examined    and 

tested 298,  299 

Describe  the  process  of  warming  up  the  engine   299 

Mention  the  various  steps  to  be  taken  in  connection  with  turning 

the  engine  over  under  steam   300 

Trace  in  detail  the  passage  of  the  steam  from  its  formation  in  the 
boilers  through  its  entire  round,  and  to  its  return  to  the  boilers 

as  feed-water • 301 

What  dispositions  are  made  when  stopping  the  engines  momentarily? 
What  if  the  stop  is  to  be  of  some  little  duration,  but  with  the 
engines  ready  for  immediate  start?  What  if  of  longer  duration 

and  steam  is  to  be  shut  off  the  engine?  303 

What  derangements  are  likely  to  occur  in  the  oiling  gear? 304 

What  causes  may  lead  to  a  hot  bearing,  and  what  measures  may  be 

taken  to  control  the  situation? 304 

What  are  the  causes  of  pounding,  and  what  measures  of  relief  may 

be  taken  ?   306 

What  are  the  evidences  of  priming  or  lifting  water,  and  what  should 

be  done  under  such  conditions? 307 

What  causes  may  lead  to  a  poor  vacuum  with  a  hot  condenser?.  ..  .  307 

What  causes  may  lead  to  a  poor  vacuum  with  a  cool  condenser? 307 

What  are  the  necessary  conditions  in  order  that  rusting  may  pro- 
ceed continuously  at  ordinary  temperatures?  308 

What    means    does    this    suggest    for    preventing   the    formation    of 

iron  rust?  308 

Describe  the  process  of  corrosion  by  an  acid 309 

Why   are   brass,   bronze   and   copper   used   for   many   fittings   which 

might  otherwise  be  made  of  iron?   ! 309 

What  is  black  or  magnetic  iron  oxide  and  how  is  it  formed? 310 

What  is  one  of  the  purposes  of  the  ferrules  sometimes  fitted  in  the 

back  ends  of  boiler  tubes? 310 

How  may  air  and  carbon  dioxide  gain  access  to  the  inside  of  a  boiler?  310 
Explain  the  nature  of  animal  and  vegetable  oils  and  how  they  may 

give  rise  to  the  formation  of  a  fatty  acid 311 

Explain    the    troubles    which    were    formerly    met    with    due    to    the 

presence  of  fatty  acids  in  boilers    311 

How  are  these  difficulties  now  avoided?    311 

What  other  acids  may  be  present  in  the  boiler? 311 

What  is  meant  by  pitting? 312 

Explain   briefly  what  is   meant   by   electro-chemical   action,   and   its 

relation  to  boiler  corrosion  312 

What  are  the  various  means  which  may  be  employed  to  reduce  or 

prevent  the  internal  corrosion  of  boilers? 315-318 

What    are    the    special    conditions    necessary    to    reduce    or    prevent 

electro-chemical  action  ? .* 316 

How  does  the  use  of  soda  aid  in  preventing  corrosion? 316 

How  does  the  use  of  zincs  aid  in  this  purpose? 317 

How  should  the  zincs  be  fitted  in  order  to  be  most  effective? 317 

Should  7.'mcs  be  fitted  in  boilers  used  for  distilling  purposes? 317 

What   treatment   should  be  applied  to  spots  in  the  boiler  showing 

marked  corrosion? 318 

Explain  the  beneficial  action  of  scale  in  preventing  corrosion 318 

What  means  may  be  taken  for  the  protection  of  boilers  which  are  to 

be  laid  up? 318 

What  is  the  proportion  of  solid  matter  in  ordinary  sea  water? 319 

What  is  the  average  composition  of  this  solid  matter? 319 

What  is  the  chief  component  of  the  solid  matter  in  ordinary  fresh 

water?    320 

What  are  the  chief  constituents  of  boiler  scale  from  river  water,  from 

brackish  water,  and  from  sea  water? 320 


690  APPENDIX. 

PAGE. 

Explain  the  manner  in  which  calcium  carbonate  is  deposited  from  so- 
lution , 321 

Explain   the   manner   in   which   calcium    sulphate   is   deposited   from 

solution    321 

What   ill   effects   may   arise   from   the   accumulation   of   scale   in   the 

boiler? 321 

State  some  of  the  various  ways  in  which  the  formation  of  fresh  water 

scale  may  be  reduced  or  prevented 322 

Explain  why  the  present  condition  with  regard  to  the  formation  of 
salt  water  scale  is  quite  different  from  that  existing  in  former 

years  with  the  very  light  steam  pressures  then  common 324 

Why  was  blowing  off  and  making  up  with  salt  feed  then  admissible, 

while   now  inadmissible ?    324 

What  is  the  present  condition  with  regard  to  make  up  feed,  and  how 

is  it  preferably  obtained  or  carried?   325 

State  some  of  the  various  ways  in  which  the  formation  of  salt  water 

scale  may  be  reduced  or  prevented 326 

In  what  manner  may  sea  water  be  prepared  for  use  in  the  boiler  by 

the  removal  of  the  scale-forming  constituents? 326 

Can  scale  formation  be  entirely  prevented,  and  if  not  what  steps  must 

be  taken  to  insure  the  safety  and  efficiency  of  the  boiler? 326 

Describe  the  combinations  of  oil  and  scale  which  may  be  formed  with- 
in a  steam  boiler 326 

What  is  the  surest  means  of  preventing  the  formation  of  such  com- 
binations?    328 

In  the  inspection  of  boilers  after  use  what  points  should  be  specially 
looked  for  in  the  furnace  fronts,  in  the  grates  and  bearers,  in  the 
bridge  wall,  in  the  tubes,  in  the  joints  and  seams,  in  the  front 

connections  and  uptakes,  in  the  bracing,  in  the  fittings? 328,  329 

What  special  points  should  be  held  in  view  in  examining  the  char- 
acter and  amount  of  scale  ?  330 

What  special  points  should  be  held  in  view  in  looking  for  corrosion?  330 

What  is  the  hydraulic  test  and  how  is  it  carried  out?  331 

What  steps  may  be  taken  in  the  case  of  leakage  about  the  joints  on 

boiler  mountings  ? 333 

What  steps  may  be  taken  in  the  case  of  leakage  about  shell  joints?  333 
What  steps  may  be  taken  in  the  case  of  leakage  about  the  various  in- 
ternal joints  of  a  Scotch  boiler?   335 

What  is  a  soft  patch  and  how  is  it  applied?  336 

What  is  a  hard  patch  and  how  is  it  applied?  336 

Describe  various  means  for  taking  care  of  small  cracks  or  holes.  ..  .  336 
What  are  blisters  and  laminations  and  what  may  be  done  with  them?  337 

How  may  leaky  tubes  be  treated?   338 

What  steps  may  be  taken  in  the  case  of  leakage  about  braces  and 

stays  ?     339 

What  steps  may  be  taken  in  the  case  of  bulging  or  collapse  of  fur- 
nace and  combustion  chamber  plates?  339 

What  may  be  done  with  a  small  split  in  the  feed  pipe? 341 

In  the   case  of  overhauling  and   repairing  the   main   engines,   what 

special  points  must  be  looked  for  in  the  cylinders?  342 

What  points  in  the  various  pin  joints  and  bearings? 343 

What  methods  may  be  used  in  adjusting  the  bearings? 344 

What  points  in  the  crosshead  and  guides?    345 

Explain  the  general  operation  of  lining  up  and  adjusting  a  ma- 
rine engine  347 

What  points  in  the  valve  gear?   352 

What  points  in  the  thrust  bearings?  353 

What  troubles  are  liable  to  be  met  with  in  the  condenser,  in  the  air- 
pump  or  in  other  pumps?  353-^-- 

Men.tion  the  spare  parts  usually  carried 356 


APPENDIX.  691 

PAGE. 

Describe  the  general  methods  in  use  in  laying  up  marine  machinery, 

and  the  points  requiring  special  care  " 356 

CHAPTER  VII. 

Valves  and  Valve  Gears. 

E\ plain  the  meaning  of  the  terms  steam  lap,  exhaust  lap,  steam  lead, 

e.\l:;,ust  lead,  cut-off,  compression  or  cushion 359 

Explain  the  general  operation  of  a  plain  slide  valve 359,  300 

What  is  a  double  ported  slide  valve,  and  what  is  the  purpose  of  this 

style    of   valve  ?    360 

What   is   a  piston  valve,   and   what   is   its  chief  advantage  over  the 

flat  slide  valve? 361 

What  is  the  purpose  of  an  equilibrium  piston  and  how  is  it  fitted  up?  365 
What  is  the  purpose  of  Joy's  assistant  cylinder  and  how  is  it  fitted  up?  366 
What  is  the  purpose  of  an  equilibrium  ring  on  the  back  of  a  flat 

slide  valve,  and  how  is  it  fitted  up?   367 

Explain  the  difference  between  an  outside  and  an  inside  valve 368 

What  is  an  excentric  and  what  is  meant  by  its  throw  and  angular 

advance? 369,  370 

Explain  the  difference  in  the  angular  location  of  the  excentric  relative 

to  the  crank  in  the  case  of  an  outside,  and  of  an  inside  valve.  .  .  .   371 
Explain  the  oval  valve  diagram  for  representing  the  movement  of 
the   valve   relative   to   the   piston,   and   for   showing  the  various 

events  and  items  of  the  operation    372 

Explain  the  influence  on  the  various  events  and  items  due  to  change 

in  the  three  items,  angular  advance,  steam  lap  and  exhaust  lap,  ,  376 
Explain  the  Bilgram  valve  diagram  for  showing  the  same  features  as 

mentioned  above  in  connection  with  the  oval  diagram 377 

Explain   the   Zeuner  valve  diagram  for  showing  the   same   features 

as  mentioned  above  in  connection  with  the  oval  diagram 379 

Describe  tVie  main  features  of  a  Stephenson  link  valve  gear 380 

When  partly  linked  up,  how  may  the  motion  of  the  valve  be  deter- 
mined ? 382 

What    is    the    difference    between    the   two    arrangements    known   as 

crossed  rods  and  open  rods?   384 

Whnt   are  the   various   effects   due   to   linking  up,   and   what   is   the 
difference  as  regards  the  lead  in  the  case  of  open  and  crossed 

rods? 385 

Describe  the  main  features  of  the  Braemme-Marshall  valve  gear....   386 

Describe  the  main  features  of  the  Joy  valve  gear 391 

Describe  the  main  features  of  the  Walschaert  valve  gear 391 

What  «".iv  the  chief  advantages  of  the  radial  types  of  valve  gear?.  ...  393 
Describe  the  main  features  of  the  crank  valve  gear,  and  explain  its 

mode  of  operation 394 

Describe  the  usual  form  of  excentric 397 

I  Fo\v  is  it  fitted  ur>  and  secured  to  the  shaft? 397 

Describe  the  usual  form  of  excentric  rod  and  strap 398,  399 

Describe  the  usual   form  of  double  bar  link,  and  the  method  of  its 

control  by  bridle   rods    400 

Describe  the  usual  form  of  link-block  and  valve-stem  402 

How  may  an  engine  be  put  on  the  center  or  dead  noint? 405 

How  would  you  set  the  main  valve  of  an  engine?  406 

In  setting  a  valve  what  will  be  the  result  of  an  incorrect  length  of 

valve  rod  ? 406 

What   will  be  the   i-ftV.M   of  an  incorrect  angular  location  of  the  ex- 
centric  relative  to  the  crank?  407 

Can  a  perfect  balance   of   steam   and   exhaust  events  and   items   be 

obtained?  407,  408 

Describe  the  general  operation  of  setting  a  valve  by  observation  of 

the  valve  itself   407 


692  APPENDIX.. 

PAGE. 

Describe    the   use    which    may   be   made    of    indicator    cards    to    the 

same    purpose    • 4°8 

CHAPTER  VIII. 

Indicators  and  Indicator  Cards. 

Describe  briefly  what  is  shown  by  an  indicator  card  and  name  the 

various  lines 410 

In  what  manner  does  an  actual  card  differ  from  an  ideal  card,  or  a 

card  referring  to  ideal  conditions?  4H 

To  what  are  these  differences  due? 4H 

What  are  the  two  chief  uses  of  indicator  cards? 412,  4*3 

As  shown  by  the  indicator  card,  what  is  the  result  on  the  steam  dis- 
tribution of  setting  the  excentric  too  far  ahead  of  a  line  at  right 
angles  to  the  crank,  that  is,  of  too  large  an  angular  advance?  ....  413 

What  is  the  result  similarly  with  too  small  an  angular  advance? 413 

What  is  the  result  with  the  steam  lap  too  large? 414 

What  is  the  result  with   steam   lap  too   small?    414 

What  is  the  result  with  exhaust  lap  too  large? 414 

What  is  the  result  with  exhaust  lap  too  small?  414 

Wrhat  is  the  result  with  excessive  compression?  415 

What  is  the  result  with  excessive  expansion? 415 

What  is  the  result  with  valve  stem  too  long  or  too  short? 415 

What  is  the  result  of  a  leaky  piston  or  piston  rod  stuffing  box? 416 

What  is  the  result  with  ports  and  passages  too  small? 416 

Describe   in   detail   the   method   of  working  up   indicator   cards   for 

power,  both  by  ordinates  and  by  the  planimeter 417 

Describe  and  explain  the  method  of  combining  a  set  of  indicator  cards 

from  a  triple  or  multiple  expansion  engine 426 

Describe  a  steam  engine  indicator,  name  its  various  parts  and  state 

their  uses 429 

What  is  the  object  of  the  reducing  motion?  * 431 

Describe  various  kinds  of  reducing  motions  431-434 

In  examining  and  adjusting  an  indicator  for  service  on  the  engine, 

what  are  the  chief  points  to  which  attention  should  be  given?  434,  435 

Describe  the  operation  of  taking  a  card 436 

How  is  the  atmospheric  line  drawn? 436 

What  information  should  be  placed  on  each  card  as  it  is  taken? 436 

CHAPTER  IX. 

Special  Topics  and  Problems. 

In  what  three  physical  states  may  bodies  exist? 43& 

Name  the  characteristics  of  each 438 

Describe  the  results  of  continually  applying  heat  to  a  lump  of  ice.  ...  439 

What  is  the  difference  between  a  gas  and  a  vapor?  440 

What  are  the  two  chief  kinds  of  change  which  the  addition  or  sub- 
traction of  heat  may  produce? 440 

What  is  meant  by  the  terms  sensible  heat  and  latent  heat,  and  how 

are  each  related  to  the  energy  of  the  molecule? 441 

What  is  meant  by  the  term  temperature? 442 

How  is  it  measured?  442 

What  thermometer  scales  are  in  use  and  how  are  they  related? 442 

How  is  heat  measured  as  to  its  quantity? 442 

What  is  the  heat  unit  employed? 443 

What  is  meant  by  Joule's  equivalent  or  the  mechanical  equivalent  of 

heat,  and  how  much  is  it? 443 

In  how  many  ways  may  heat  be  transferred  from  one  body  or  place 

to  another?    444 

Describe  radiation,  conduction  and  convection 444 

Describe  emission  and  absorption 444 


APPENDIX.  695 

PAGE. 

Describe  how  these  verious  operations  enter  into  the  heating  of  the 

water  in   a  boiler 444 

Describe  the  formation  of  steam  from  water 445 

How     does     the     temperature     of     the     boiling     point     vary     with 

the    pressure  ? 44& 

What  is  saturated  steam?. 44& 

What  is  moist  or  wet  steam  ? 44$ 

What  is  dry  and  saturated  steam?  449 

What  is  superheated  steam? 449 

What  is  meant  by  the  total  heat  of  steam?   45O 

How  do  you  find  the  total  heat  of  a  mixture  of  steam  and  water?   .  .  451 
Mention  various  ways  in  which  the  economy  of  a  steam  boiler  may 

be    considered 453 

Describe  in  particular  the  conditions  affecting  fuel  economy 454 

What  is  meant  by  the  evaporation  per  pound  of  coal,  and  how  is 

it    found  ?   456 

What  is  meant  by  the   evaporation  per  pound  of  combustible,  and 

how  is  it  found? 459 

Describe  the  cycle  or  routine   corresponding  to  the  so-called  ideal 

engine     461 

Upon  what  does  the  efficiency  of  such  an  engine  depend?   462 

Describe   the  various   heat   wastes  which   prevent  the  actual   engine 

from  realizing  the  efficiency  of  the  ideal 464 

In  what  fundamental  ways  may  the   efficiency  of  the  actual  engine 

be    improved  ?   465 

In  particular   what    methods    may   be    taken   for    reducing   the   heat 

wastes  of  actual  engines?  465-468 

Explain  the  gains  which  may  result  from  the  use  of  superheaters,  re- 
heaters,  jackets,  feed  heaters • 467 

Explain  the  relation  of  expansion  to  gain  in  efficiency 469 

State  for  various  representative  types  of  engines  the  economy  which 
may  be  expected  in  terms  of  coal  per  I.H.P.  per  hour  and  Ibs. 

of  steam  per  I.H.P.  per  hour 471 

Derive  the  formulae  required  for  a  general  discussion  of  the  lever 

safety  valve   447-480 

Explain  the  suppositions  made  in  connection  with  the  subject  of 
boiler  bracing,  and  show  how  the  principles  of  mechanics  are 

applied  to  these  problems 480-484 

Derive  the  formulae  for  the  strength  of  cylindrical  boilers,  for  both 
longitudinal  and  for  circumferential  rupture,  and  show  that, 
aside  from  the  influence  of  the  riveted  joints,  the  boiler  is  twice 

as  strong  in  the  latter  as  in  the  former  direction 485-488 

Derive  the  formulae  for  the  strength  of  a  bumped  boiler  head 488 

Derive  the  formulae  required  for  the  discussion  of  the  loss  by  blow- 
ing off,  and  show  how  to  apply  it  to  special  cases 489 

Explain  the  operation  of  the  different  types  of  feed  water  heaters, 

and  how  they  may  effect  a  saving  in  the  heat  required   .  ..  .255.  491 
How    may    the    various    diameters    for   the    cylinders    of   triple    and 

quadruple  expansion  engines  be  proportioned? 492 

What  is  a  clearance  volume  ?  494 

Describe  methods  for  its  determination 495 

How  does  the  clearance  affect  the  apparent  expansion  ratio  as  given 

by  the  point  of  cut-off? 496 

Whit  is  the  "engine  constant"  for  power,  and  how  is  it  found? 497 

What  is  meant  by  the  term  "indicated  thrust,"  and  how  is  it  found?.  .  498 
What  is  meant  by  the  expression  "reduced  mean  effective  pressure" 

or  "mean  pressure  reduced  to  the  L.P.  piston"?  499 

How  is  .this  reduced  pressure  found,  and  what  is  its  relation  to  the 

indicated    thrust  ?   500-501 

How  may  we  compute  the  load  on  the  main  guides?   502 

How  may  we  compute  the  force  required  to  move  a  slide  valve?.  ..  .  503 


694  APPENDIX. 

PAGE. 

How  may  we  compute  the  number  of  pounds  of  condensing  water 

per  pound  of  steam  for  any  given  set  of  conditions?  504 

How  may  we  compute  the  work  done  by  pumps,  knowing  the  de- 
livery head  and  the  amount  of  water  handled?  505-50? 

How  may  we  compute  the  discharge  of  steam  from  an  orifice? 507 

Explain  some  of  the  short  cuts  and  convenient  methods  which  may 
be  employed  in  the  computation  of  the  weights  of  parts  of 
marine  machinery  508-512 

CHAPTER  X. 

Propulsion  and  Powering. 

What  is  the  unit  of  speed  used  in  navigation,  and  what  is  its  value 

in  feet  per  hour  ?  5*4 

How  may  knots  be  reduced  to  feet  per  minute?   514 

How  may  miles  per  hour  be  reduced  to  feet  per  minute?   514 

Explain  briefly  the  fundamental  problem  in  propulsion 515 

Describe  a  screw  propeller,  and  name  its  various  parts  and  pro- 
portions    5X7 

What  is  slip  or  slip  ratio,  and  how  is  it  computed? 519 

What  is  the  condition  of  the  water  in  which  the  propeller  works?  520 
What  is  the  difference  between  the  true  slip  and  the  apparent  slip?. .  .  521 

Describe  various  forms  of  screw  propellers 523 

When  the  blades  are  east  separately,  how  are  they  secured  to  the  hub?  524 

Describe  the  attachment  of  the  propeller  to  the  shaft 525 

What  materials  are  used  for  screw  propellers?  526 

Describe  methods  of  measuring  the  pitch  of  a  screw  propeller.  . .  .526-529 

Describe  the  radial  paddle  wheel 530 

Describe  the  feathering  paddle  wheel 530 

Describe  the  two  methods  employed  for  operating  the  floats  in  the 

feathering  wheel    530 

What  is  the  "rolling  circle"  ?  533 

How  is  the  slip  of  the  paddle  wheel  estimated? 533 

Give  the  Admiralty  coefficient  formula  for  powering  ships 534 

In  general,  how  does  the  coefficint  vary  with  the  speed  and  geo- 
metrical characteristics  of  the  ship?  53=; 

Name  average  values  for  typical  cases 536 

Explain  the  reduction  of  power  developed  by  a  ship  when  towing, 

or  when  undergoing  a  dock  trial 537 

W'hat  are  the  general  purposes  of  trial  trips? 539 

For  the  determination  of  speed  alone,  what  observations  are  neces- 
sary?  540 

Describe  various  ways  in  which  tidal  influence  may  be  eliminated  540-542 
Describe  the  manner  in  which  such  information  may  be  plotted  or 

represented  graphically 541-543 

Describe  the  various  conditions  which  should  be  attended  to  in  trials 

intended  to  develop  the  maximum  speed  and  power 544 

CHAPTER  XI. 

Refrigeration. 

Explain   the    general    principles   of   refrigeration 545 

How  are  these  principles  carried  out  by  the  use  of  freezing  mixtures?  546 
How  are  they  carried  out  by  the  use  of  ammonia  or  similar  sub- 
stances ?     547 

Give  the  principal  features  of  ammonia  refrigerating  apparatus  and 

explain  its  operation 549 

How  are  the  principles  of  refrigeration  carried  out  by  the  use  of  a 

compressed    gas? 553 

Give  the  principal  features  of  compressed  air  refrigerating  machinery 

and  explain  its  operation 554 


APPENDIX.  695 

PAGE. 

"What  special  points  must  be  attended  to  in  the  operation  and  care  of 

refrigerating    machinery?   556 

CHAPTER  XII. 

Electricity  on,. Shipboard. 

Explain  the  fundamental  properties  of  a  common  magnet 559 

What  principle  serves  to  connect  magnetism  with  electric  currents?  561 
Whur   are   the   fundamental   principles  upon   which   the   operation   of 

the  electric   generator  depends?   562 

Define   the    following  terms:     Electro-motive   force,   volt  resistance, 

Ohm,  Ampere,  Watt 563-564 

What  are  the  two  leading  subdivisions  of  electric  machinery? 565 

Which  form  is  commonly  used  on  shipboard? 566 

What  are  the  leading  features  of  a  modern  marine  generating  set?  567 

How  does  a  motor  differ  from  a  generator?   570 

For  what  are  motors  chiefly  used?   570 

Explain   the   method   of   distribution    of   electric   current    for   incan- 
descent lamps  572 

What  is  the  purpose  of  the  switchboard?   573 

Mertion  the  chief  instruments  and  appliances  found  on  the  switch- 
board and  give  their  uses 573~574 

Describe  the  usual  type  of  incandescent  lamp 575 

Describe  a  simple  type  of  arc  lamp 576 

What   points  are  of  chief  importance  in  the  operation  and  care  of 

electrical  machinery  ? 577 

What  are  faults    and  how  may  they  be  located? 578,  580 


INDEX.  697 


Index. 


Adamson  ring 94 

Adjustment  of  bearings  230,  344 

Adjustment    of    engines    341 

Air  casing    107 

Air  lock   133 

Air  pump    245 

Air  pump  valve   248 

Alloys  , 24 

Almy  boiler 54 

Aluminum  I 

Ammonia  refrigerating  apparatus 549 

Angle  valve   213 

Antimony  I 

Arrangement  plans,  general 271 

Arrangements  of  cylinders 164 

Ash  ejector   269 

Ash  gun    270 

Ash  pit  door  104 

Ashes,  disposal  of 282 

Auxiliaries   241 

Babcpck  and  Wilcox  boilers 65 

Beading  tool  92 

Beam  engine    162 

Bearing  bars    104 

Bearing,  hot   3°4 

Bearings    19° 

Bearings,   adjustment   of 230,  344 

Bedplates    172 

Belleville  boiler  66 

Bending  tests   29 

Bessemer  process   13 

Bilgram  valve  diagram  378 

Bismuth    I 

Blisters  and  laminations  1 1 

Blowers    267 

Blowing  off 281 

Blowing  off,  loss  by 489 

Blow-off  cock    " 122 

Boilers 47 

Boiler  brace  problem   480 

Boiler  bracing  94,  100 

Boiler  construction   ' 86 

Boiler  corrosion    308 

Boiler  design  in  accordance  with  U.  S.  Rules 138 


698  INDEX. 

PAGE. 

Boiler  economy   453 

Boiler  heads   146 

Boiler  lagging   129 

Boiler  mountings   115 

Boiler  overhauling  and  repairs 328 

Boiler-room  routine  273 

Boiler   saddles    128 

Boiler  scale 319 

Boiler  test   331 

Boiler  tubes,  leakage  in 295 

Boilers,  laying  up 318 

Boilers,  relative  advantages  of  different  types  56 

Boilers,  strength  of  485 

Boilers,  weights  of   1 12 

Bottom  blow 122 

Bourdon  steam  gauge   124 

Bowling  ring    94 

Brace,  boiler,  problem    480 

Braces,  boiler   94 

Braemme  Marshall  valve  gear  386 

Brazing  copper  joint  2 

Bridge  wall 104 

Bridle  rods   401 

Briquettes 41 

Bucket  valve?  246 

Built-up  crank  shaft  186 

Bulging  or  collapse  of  furnace  and  combustion  chamber  plates 339 

Bumped  heads   146 

Butt  straps   138 

Butterfly  valve   210 

Calking  tools  87 

Carbon,  influence  of  on  cast  iron 4 

Cast  iron    4 

Casualties  and  emergencies  in  fire-room 287 

Center,  putting  an  engine  on 405 

Center  of  gravity  658 

Centrifugal  pumps    241 

Check  valve 121 

Check  valve  jammed  291 

Chrome  steel  23 

Chromium,  influence  of  on  cast  iron 7 

Circulating  pumps   241 

Cleaning  fires 282 

Clearance  and  its  determination 494 

Clearance,  effect  of  in  modifying  the  apparent  expansion  ratio 496 

Clinker,  formation  of   35 

Coal    31 

Coal  consumption,   problems    472 

Coil  and  tubulous  boilers  152 

Collc.pse  of  furnace  crowns  or  combustion  chamber  plates 294 

(  ollapse  or  bulging  of  furnace  and  combustion  chamber  plates 339 

Columns  168 

Combined  indicator  cards  425 

Combustion    32 

Combustion  chamber 89 

Coming  into  port   286 

Common  fractions  581 

Compound  engine   155,  157 

Compressed  air  'refrigerating  machinery 554 

Compressed  grease  cup   233 

Computations  for  engineers   581 


INDEX.  699 

PAGE. 

Computing  weights  of  machinery 508 

Concaved  heads   147 

Condenser  tube  packing 246 

Condensers  243 

Condensing  water,  amount  required 504 

Connecting  rod   184 

Copper    2 

Corrosion 308 

Corrugated  furnace  flues    141 

Corrugated  furnaces 88 

Corrugation,  styles  of 88 

Counter  gear  227 

Cracks  and  holes 336 

Crank  valve  gear  393 

Crankshaft 185 

Crosshead  marks   , 346 

Crossheads    180 

Crown   bar    99,  145 

Crucible   steel    ,     13 

Cylinders 165 

Dead  plate  104 

Decimal   fractions 592 

Direct    act  ing    pumps 263 

Direct  tubular  boiler  50 

Disc  valve  with  balance  piston 211 

Distribution  of  power  in  a  multiple  expansion  engine 428 

Dock  trial,  reduced  power  at 537 

Doctor  on  western  river  boats 204 

Double  beat  poppet  valve 210 

Double  end  boiler 50 

Double  ported  slide  valve 360 

Downflow  pipes    53 

Draft     129 

Draft    gauge    130 

Drain  gear   215 

Dry  pipe    120 

Duodecimals      615 

Dynamo,   electric    565 

Fconomy,  steam  boiler 453 

Economy,  steam  engine  460,  471 

Elastic  limit    . 26 

Electric  generator   565 

Electric   lamps    575 

Electric  machinery,  faults  in 578 

Flfctrical  machinery,  operation  and  care  of 577 

Electric  motors    570 

Electricity  on  shipboard  559 

Ellis  and   Eaves  draft 135 

Elongation    26 

Emergencies  and  casualties  in  fire-room 287 

Fmergencies   in   engine  room 304 

Engine  constant 407 

Engine  economy    460 

Engine  fittings    209 

Engine  overhauling,  adjustment  and  repairs 241 

Engine  room  routine  and  management 298 

Equilibrium  piston  365 

Evaporation   per  pound  of  coal 455 

F.vanoration  per  pound  of  combustible 459 

Evaporators    261 

Excentric 397 


700  INDEX. 

PAGE. 

Excentric  rod 397 

Excentric  strap    397 

Expansion  joint 239 

Expansion  of  steam,  relation  to  economy 469 

Fans    267 

Feed   check 121 

Feed  heaters    255 

Feed  pipe,  split  in 341 

Feed  pump    , 251 

Feed  pump   disabled    288 

Feed  water  heating,  gain  by 491 

Ferrule,  condenser  tube 245 

Ferrules,  boiler  tube 93 

Filters    260 

Fire-room  routine 277 

Fire-tube  boiler   48 

Fires,  cleaning  the   282 

Firing 277 

Flange   coupling 188 

Flexible  coupling   188 

Flue  and  return  tube  boiler 51 

Flue  boilers   52,  113 

Foaming    287 

Foot  valves    246 

Forced  draft   132 

Forged  crank  shaft 187 

Front   connections 106 

Fuels    31 

Funnel    106 

Furnace  doors   102 

Furnace  fronts  102 

Fusible  plug   148 

Gain  by  feed  water  heating 491 

Gate  valve 214 

Gauge  cocks   148 

Gauge   glass,  bursting  of 291 

General  arrangement  of  machinery 271 

Geometrical  problems   , 642 

Geometry  and  mensuration    621 

Getting  under  way 273,  298 

Girder  brace    99 

Globe  valve    213 

Governors    225 

Grate    104 

Grate  bars   105 

Grease  cup,  compression   233 

Gridiron  valve   210 

Guides,  main  190 

Gusset  brace    100 

Hammer  tests  29 

Hard  patch   336 

Head  valves  246 

Heat  and  the  formation  of  steam 438 

Heat,  its  relation  to  matter 439 

Heat,  total  of  steam 450 

Heat  unit  442 

Horizontal  back  acting  engine 159 

Horizontal  direct  acting  engine 159 

Hot  bearing  304 

Howden  draft 133 

Hydrokineter    '. 127 


INDEX.  7oi 

PAGE. 

Hydrometer  I27 

Ideal  indicator  card  412 

Inclined  engine  I6° 

Indicated  thrust  49$ 

Indicator  card,  operation  of  taking 434 

Indicator  cards  with  deranged  valve  gear 4:3 

Indicator  cards,  working  up  for  power 41? 

Indicators  and  indicator  cards 4IQ 

Indicators,  steam  engine 429 

Induced  draft   135 

Injector    254 

Inside  valve   368 

Iron    3 

Joint,   expansion    239 

Joints   and   packing    220 

Joints  boiler 86 

Joints,    riveted    67 

Joy  radial  valve  gear  39° 

Joy's  assistant  cylinder  366 

Lagging,  boiler   129 

Lagging,  engine   228 

Lagrafel  and  D'Allest  boiler 64 

Lap  359 

Latent  heat 44i>  452 

Laying   up    boilers 318 

Laying  up  marine  machinery 356 

Lead    23 

Lead   of  a  valve 359 

Leakage  about  stays  and  braces 339 

Leakage    at    internal    joints 335 

Leakage  in  boiler  tubes 295 

Leg  boiler   51 

Lever  safety  valve 115 

Lever    safety   valve    problem 476 

Line  shaft  bearing 193 

Liners    166,  167 

Lining  up  engines 347 

Linings < 144 

Link   block    402 

Link,  Stephenson   400 

Liquid   fuel    42 

Liquid  fuel,  use  of,  combined  with  coal  46 

Locomotive  patch  336 

Locomotive  type  boiler 51 

Loss  by  blowing  off 489 

Low  water -. 292 

Lubricants    228 

Lubrication   and   oiling  gear 228 

Lubricator  233 

Main  guides,  pressure  on 502 

Malleable  iron    Q 

Manganese,  influence  of  on  cast  iron 7 

Manganese,  influence  of  on  steel 15 

Manhole  covers    I0i 

Manhole  fitting   ]   IOI 

Manholes 

Marine  engines 
Marshall  valve  gear 

Materials  of  construction  strength  of 30 

Mean    effective   pressure   by   planimeter 421 

Mean  effective  pressure  from  indicator  card Ig 


702  INDEX. 

PAGE. 

Measures  and  weights 599 

Mechanical  powers 659 

Mechanics    652 

Mensuration    621 

Metallic  packing  223 

Monkey  tail  valve  216 

Mosher  boiler  57 

Muffler    118 

Multiple  expansion  engines,  proportions  of  cylinders  for 492 

Mushet  steel  23 

Nickel  steel  22 

Niclausse  boiler 63 

Normand   boiler    61 

Oil  and  scale 326 

Oil  cup,  sight  feed 233 

Oil  cup   with   adjustable   feed 232 

Oil  distribution,   modern  systems   of 235 

Oil  fuel 42 

Oil  pump   235 

Oiling  gear 228 

Oiling  gear,  derangement  of 304 

Open  hearth  process 14 

Oscillating  engine 159,  161 

Outboard  discharge  valve 242 

Outboard  shaft    189 

Overhauling  of  engines 341 

Packing    220 

Packing,  condenser  tube 245 

Paddle  wheel,  feathering 530 

Paddle  wheels 530 

Passover  valve  216 

Patch  for  boiler  tube  sheet '.   337 

Patch  for  leaky  j  oint 334 

Patch,  hard,  soft,  locomotive 336 

Percentage    596 

Phosphorus,  influence  of  on  steel 15 

Physics    650 

Pillow  block,  main 191,  192 

Piping   237 

Piston    175 

Piston,  equilibrium   365 

Piston  rings 176 

Piston  rods    '. 179 

Piston  valve 361 

Pitch,  measurement  of 526 

Pitting   312 

Planimeter,  use  of  for  working  up  indicator  cards 421 

Plunger    p'ump    251 

Poppet  valve 210 

Port,  coming  into  286 

•Pounding   306 

Powering  ships   534 

Pressure  allowed  on  cylindrical  shell  boilers 138 

Priming    287,  307 

Propellers,  materials  of 526 

Propeller,    screw 517 

Propellers,  varieties  of 523 

Proportion 607 

Proportions  of  cylinders  for  multiple  expansion  engines 492 

Propulsion 514 

Propulsion  and  powering 514 


INDEX.  703 

PAGE. 

Packing,  metallic 223 

Pump,  Admiralty 264 

Pump,  air 245 

Pump,  duplex 264 

Pump,  oil 235 

Pump,  plunger  251 

Pumps,  centrifugal   241 

Pumps,  circulating  241 

1 '111111)8,  direct  acting 263 

Pumps,  feed 251 

Pumps,  work  done  by 5°4 

Quenching  tests 29 

Ramsbottom  rings 177,  178 

Ratio  and  proportion 607 

Reduced  mean  effective  pressure 499 

Reducing  motions 430 

R  eduction  of  area  27 

Refrigeration    545 

Refrigeration  by  expansion  of  a  compressed  gas 553 

Refrigeration  by  freezing  mixtures 546 

Refrigeration  by  vaporization  and  expansion 547 

Refrigerating  machinery,  operation  and  care  of 556 

Reheaters 225 

Reinforce  plate 100 

Relief  valves   215 

Repair  of  engines 341 

R  epairs.  boiler 328,  333 

Retarders  93 

Reverse  shaft   400 

Reversing  gear    217 

Ribbed  furnace  flues 142 

Rivet  holes  to  be  drilled 138 

Riveted  joints 67 

Roberts  boiler    55 

Rock  shaft 400 

Routine,   boiler   room 273 

Routine  in  engine  room 298,  301 

Rupture  of  furnace  crowns  or  combustion  chamber  plates 295 

Rm>tnre  of  steam  pipe 297 

Saddles    128 

Safety  plugs   148 

Safety  valve  problem    476 

Safety  valves    115,  i./ifl 

Saturation,   taking  the 282 

Scale,   boiler    319 

Scale  prevention,  fresh  water 322 

Scale  prevention,  salt  water 324 

Scotch    boilers 50 

Scotch  boilers,  common  proportions  of 112 

Scotch  boilers,  common  si/es  and  dimensions no 

Screw  stay  bolt 08 

Srnlmry  boiler 62 

Seatings    174 

Semi-steel    16 

Sensible  heat  441 

Separators    267 

Serve  tube   93 

Setting  a  valve   406,  408 

Ships,   powering   534 

Shrinkage  of  cast  iron   7 

Side  rods   401 


7o4  INDEX. 

PAGE. 

Sight  feed  oil  cup 233 

Silicon,  influence  of  on  cast  iron 5 

Silicon,  influence  of  on  steel IS 

Single-end  boiler  •  50 

Slide  valve,  force  required  to  move 5°3 

Slide  valves    35$ 

Slipper  crosshead  180,  181 

Smoke,  formation  of  33 

Socket  bolt    98 

Socket  coupling  190 

Soft  patch   ' 336 

Soot,  formation  of 33 

Spare  parts   '. 356 

Specifications  for  structural  steel 17 

Speed,  measure  of 514 

Spontaneous  combustion    37 

Spring  bearing  193 

Spring  safety  valve    1 16 

Starting  fires  273 

Starting  valves  216 

Stay  tubes    92 

Stays  and  flat  surfaces 139 

Stays,  boiler  94,  100 

Steam   444 

Steam  chimney  51 

Steam,  discharge  of  through  an  orifice 507 

Steam,  formation  of 438,  445 

Steam  gauge 124 

Steam  pipe,  copper 150 

Steam  pipe  rupture  of : 297 

Steam  pipe,  steel  and  iron 150 

Steam,  saturated 448 

Steam,   superheated   448 

Steam,  total  heat  of 450 

Steel  12 

Steel,  mechanical  properties  of 16 

Stephenson    link   valve    gear 380 

Stephenson  link  valve  gear,  details  of 397 

Stern  bearing  196 

Stern  brackets 198,  199 

Stern  tube   197 

Stop  valve 1 18 

Stop  valve,   main    212 

Stopping  suddenly    284 

Straightway  valve 214 

Strength  of  boilers  48^ 

Strength  of  the  useful  metals 30 

Stuffing  box   222 

Sulphur,  influence  of  on  cast  iron 6 

vSulphur,  influence  of  on  steel T5 

Surface  blow I22 

Sweeping  tubes    283 

Temperature     442 

Tempering  steel   22 

Test  of  boilers   ^j 

Test  pieces  for  iron 

Test  pieces  for  steel  and  other  materials 28 

Test  pressure T-^g 

Testing  of  metals   •. 26 

Thornycroft   boiler    \'     58 

Throttle,  operated  by  power 212 


INDEX.  7°5 

PAGE. 

Throttle  valve   209 

Thrust  bearing   IQ3>  195 

Thrust   shaft    IQ4 

Tin    24 

To.wing,  reduction  of  power  when 537 

Trial   trips    539 

Trial  trips,  special  conditions  for 544 

Triple    expansion    engine    156,  15° 

Trunk  engine   163 

Tube  expander   9° 

Tubes,    boiler    91 

Tubes,    repairs    on 338 

Tubes,  stay   92 

Tungsten  steel   23 

Turbine,  steam  207 

Turning  gear    220 

Ultimate  strength   26 

Umbrella    107 

Unstayed  flat  heads 146 

Uptakes  106 

Vacuum  falls 307 

Valves  and  valve  gears 358 

Valve,  angle   213 

Valves,  bucket    246 

Valve,  butterfly   210 

Valve   diagram,   Bilgram 378 

Valve  diagram,  oval 372 

Valve  diagram.  Zeuner  379 

Valve,  disc  with  balance  piston 211 

Valves,  foot 246 

Valve,   gate    214 

Valve  gear,  Braemme-Marshall  386 

Valve  gear,  crank 393 

Valve  gear,  Joy   3QO 

Valve  gear,   Steohenson  link 380 

Valve  gear,  Walschaert 391 

Valve,  globe    213 

Valve,  gridiron   210 

Valves,  head 246 

Valve,  main  stop   212 

Valve,  monkey  tail  216 

Valve  motion  by  simple  excentric  369 

Valve,  outboard  discharge   242 

Valve,   passover   216 

Valve,  piston 361 

Valve,  poppet  210 

Valves,  relief 215 

Valve   setting   405 

Valves,  slide   358 

Valves,  starting  216 

Valve  stem    402 

Valve  stem  guide   403.  404 

Valve,  straightway 214 

Valve,   throttle    209 

\Vatn w  top  boiler  51 

Walschaert   valve   gear    391 

Water  gauge   glass,  bursting  of 291 

Water  gauges  and  cocks 124 

Water  tending   279 

Water  tube  boiler 53 

Water  tube  boilers,  casualties  with 297 


7o6  INDEX. 

PAGE. 

Water  tube  boilers,  construction  of 108 

Water  tube  boilers,   hints  regarding  management 285 

Weathering  of  coal 36 

Weigh  shaft 400 

Weights  and  measures 599 

Weights  of  boilers 60,  112 

Weights  of  machinery,  computing 508 

Western  river  boat  "doctor" 204 

Western  river  boat  valve  gear 202 

Western  river  boat  engines 199 

Western  river  boat  boilers 113 

Wick  cup  230 

Wiper    231 

Wiring  and  distribution  of  light  and  power 571 

Wrought  iron 10 

Yarrow  boiler 59 

Zeuner  valve  diagram 379 

Zinc    . . . 24 


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